Autobiography of Piergiorgio Casavecchia: Forty Years of Happily

Special Issue Preface pubs.acs.org/JPCA

Autobiography of Piergiorgio Casavecchia: Forty Years of Happily Crossing Beams

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n 2009 The Journal of Physical Chemistry A published a Festschrift for Vincenzo Aquilanti which was longer than 1000 pages (December 31, 2009, Vol. 113, Issue 52, 14181− 15410). In his autobiography Enzo gave a personal and detailed account of the “origins” of the Molecular Beam group at the University of Perugia and summarized his outstanding contributions to the growth of the group’s activity over four decades. As Emeritus and member of the “Accademia dei Lincei” he still continues today to be very active, both nationally and internationally. A chronicle of the period in Rome that preceded Enzo’s entrance into the science world and preluded the birth of the Molecular Beam group in Perugia can also be found in a vivid account given by Gian Gualberto Volpi, mentor of Enzo Aquilanti and founder of the Perugia Molecular Beam group, in an article for Annu. Rev. Phys. Chem. (1999, Vol. 50, pp 23−50) together with Giovanni Boato. It is certainly an honor and privilege to have today a Festschrift issue of The Journal of Physical Chemistry A dedicated to the oldest of Aquilanti’s students, myself and Antonio Laganà, who are expressing the two scientific sides that Aquilanti has always manifested, represented, and worked for during his career: experiment and theory. We thank George Schatz for this opportunity. The following is a personal account of my contribution, over the past 40 years, to the development of molecular beam science in Perugia.

him for his enthusiasm, seriousness, generosity, and honesty). During this time he was exposed and sensitized toward the importance of school and education. When I entered elementary school I immediately felt my parents’ concern this way; they bought for us children a large encyclopedia that my mother still owns. My father was always very busy with work and politics and my mother was following us closely in our school endeavors. An intelligent and loving mother plays an important role (in Italy one goes to school only in the morning, so all studying is done at home in the afternoon and evening). I have always loved school and since second grade I started to excel in my class, a status that turned out to be fairly easy for me to maintain throughout my university studies. I always remember when I was in third grade and every time an educated friend of my parents would visit us he would “interrogate” me in history and other subjects that he knew I was starting to learn at that time (I felt I had to always be prepared in order to give good answers). In fourth grade the teacher sometimes asked me to help her in asking math questions to my classmates (simple ones, as one can imagine) during group interrogations. Overall, I had the luck to have a wonderful teacher in elementary school (she was like a severe mother, devoted to her mission) and excellent professors in junior high (Italian, Latin, history, geography, math, and French), where in the first and second years I loved to translate pieces of the De bello Gallico (by Julius Caesar) and read the Iliad and Odyssey by Homer. The professor of Italian in the first year of junior high at the colloquium with parents asked my mother, “Is Piero an only child?” “No,” my mother replied, “he has a younger brother and sister.” “Good, Piero will be a good example for them” was the comment. This impressed my mother and this is the story that she, at the age of 87, keeps repeating to me often. My father, unfortunately, passed away in 2000, and since then my perception of life has changed, as anyone who has lost his father can understand. He had done so much for his family and friends. Among all teachers, the professor of Italian of the third year of junior high left the largest imprint on me. I had the great pleasure to bump into him occasionally, after he retired, walking in the streets of Perugia, while I was a chemistry student at university. I would update him on the progress with my studies and he was always of continuous stimulus to me. In 1964 I choose a technical high school in chemistry, so, at the age of 15 I started to be exposed to what was to be the center of my life. Again, I was lucky to have excellent and stimulating professors. The young physics professor who had just graduated in chemistry from Bologna introduced me to physics in the first year, then to physical chemistry lab in the fifth year. He eventually became president of the school for the next 40 years. Another one, the professor

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PRE-UNIVERSITY I was born in the countryside of the small village of Compignano, near Marsciano, about 30 km from Perugia. When I was about two years old my parents left the farm life and settled in Ponte San Giovanni, a suburb of Perugia where my father had found a job with the Perugia City Hall. I essentially grew up in Ponte San Giovanni and lived there until I finished university. There, I went to kindergarten, elementary school, and junior high school and then attended high school and university in Perugia (only six kilometers away). Life in postwar Italy of the early 1950s was not as it is today. Coming from a rural area and having had to stop their schooling quite early, my parents had to rebuild their lives from scratch. My father Renzo and mother Maria Coli (known to everyone as Rosanna) have been the most dear and generous parents one could wish for; they devoted their lives to bringing up three children (my brother, Fausto, one year younger, and my sister, Grazia, six years younger) and making sure we could all go to university. This meant that they never could afford typical summer vacations. I did my part in this endeavor by trying to be a good and responsible student all along, working during high school summer vacations in the administration of a small beer-bottling and soft drinks factory and during university doing some book-keeping for my father’s dear friend, Renzo Scopetta, who owned a hardware store. In addition, I always had a fellowship that covered university books and tax expenses. My father became interested in politics when we moved to Perugia thanks to the many friends he made (everyone loved © 2016 Piergiorgio Casavecchia

Special Issue: Piergiorgio Casavecchia and Antonio Lagana Festschrift Published: July 14, 2016 4568

DOI: 10.1021/acs.jpca.6b04600 J. Phys. Chem. A 2016, 120, 4568−4579

The Journal of Physical Chemistry A

Special Issue Preface

of chemical plants, suggested to me to get two university degrees if I wanted to work in a chemical company, one in chemistry and one in engineering, because I would have acquired both ways of thinking. In the first two years I also learned technical drawing, something that I was good at (while I was not very good at drawing flowers or portraits). I could not imagine that this early learning of the subject, together with another class that I took in the first year of university, would have one day been extremely useful to me when I would have to draw a crossed beam apparatus and all its components for machine shops (in 1980 there was no AutoCAD or SolidWorks). It was great to learn some physics, mathematics, and a lot of chemistry (inorganic, organic, physical chemistry), also through laboratories. The nice thing about graduating from high school (1969) with the highest score of the school was that I was selected along with many other students from all parts of Italy to attend a two-week national preuniversity orientation course at the international Ettore Majorana Physics Center in Erice (Sicily), run by Italian particle physicist Antonino Zichichi. It was exciting: We were exposed to lectures of leading university professors in a variety of fields and had a lot of fun in that special place (a kind of Mount Olympus, for people who know the placethey regularly held there, and still do today, international scientific meetings and schools, especially in physics). But I had already made my choice. The high school experience made it very smooth for me to enter into five years of university studies in chemistry. Studying chemical engineering was also of much interest to me, but I had to rule this out because it would have meant to go to the University of Bologna which my parents could not afford.

I obtained my degree (Laurea) in chemistry at the end of July 1974 with Aquilanti. That same year an important reform of the Italian University system entered into action and fellowships for scientific and didactic formation (four years) were established (this was equivalent to what in the 1980s would have become the Ph.D. School in the Italian system, still nonexisting in the 1970s); in September three of them were offered in the chemistry department at Perugia. Of the initial group of 83, only two students got their “Laurea” cum laude in the July session of 1974, and so Mario Casciola (now an inorganic chemistry colleague in Perugia) and I readily got two of the three fellowships. It was at the same time that also Antonio Laganà started his career in the group with a researcher position established within the same university reform. In those years also other people started their career in Volpi’s group: Bruno Brunetti, Fernando Pirani, and Gaia Grossi (now all professors of general and inorganic chemistry). It was with great enthusiasm that on November 1, 1974 I started my official research activity in the molecular beam field working with Enzo Aquilanti on inelastic ion-atom collisions. That was a lucky month in my life because on November 25 (Santa Caterina’s day) I was invited to a special party at the house of Sandra Giovagnoli (a young assistant professor of mathematics) who had as a roommate Jocelyn Rix, a young English student of Italian at the University for Foreigners of Perugia. Jocelyn and Sandra had planned a Santa Caterina’s day party, and Sandra, who I did not yet personally know, had invited her friend and older colleague of mine, Bruno Brunetti, who the year before had already started his research career in Volpi’s group working with Giorgio Liuti on kinetics experiments. He had been asked to bring a friend because there would have been many foreign “female” students from the University for Foreigners. So, Bruno told me about this party in the afternoon, while we were working in two laboratories next door. In the evening we went to the party in “Via della Sposa” (Bride Street): It was that Monday evening, on the 25th of November, that I met the woman of my life! Among the many girls present, there was one in particular who captured my attention: a young American girl who was taking a three month course of Introductory Italian at the University for Foreigners and was in the same class and good friend of Jocelyn Rix (who still sends us a wonderful letter/card every year since and sometimes also calls us for the Santa Caterina’s anniversary). With Stephanie Seymour, from Los Angeles, it was love at first sight! We went out for dinner two days later, and since then we have always been together. I can certainly say today (but I felt it since the beginning) that an artist is the perfect wife for a scientist! I was always exposed to the two wonderful worlds of science and art! Sandra, and later on her husband Derek Boothman, has remained very meaningful to Stephanie and me. They were professors at the University of Perugia first and later on in Bologna. They retired recently, and once in a while we still see each other with great pleasure. Bruno has remained my closest friend and a very meaningful one for both myself and Stephanie. Bruno started on kinetics with Liuti, then moved to Penning ionization and intermolecular forces and finally (around 2000) to applications of chemistry to art preservation, where he has expressed all his talent, expertise, and love for art by coordinating several large European research infrastructure networks on this new research line (Cultural Heritage) up to the present day. During my first three years in Perugia I used and improved the original experimental apparatus set up by Aquilanti, where

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UNIVERSITY TIMES AND BEGINNING IN RESEARCH In November 1969 I entered the University in Perugia. I remember the first class was a general chemistry class given by professor Volpi, of 83 students. The first two exams I did at the end of the first year were with professors Gian Gualberto Volpi and Vincenzo Aquilanti (his assistant at that time): Certainly I did not predict that day that five years later I would have joined their research group! In the fifth year of chemistry studies one is supposed to do a Master’s thesis. At that time there was a strong quantum chemistry group in the department, and several students, after their degree, had taken fellowships to continue to do research in that area. One of these young quantum chemists, Elvio Semprini, was the step-son of my third year junior high professor of Italian: I knew about him and had met him on a couple of occasions while he was strolling in the city with my old professor. He suggested to me to do my Master’s thesis in a large group, and that of Volpi, who had set up a modern line of research, was one of the two options that he recommended. This choice was the turn of my life, because as I entered into scientific research I realized that this was what I wanted to do in life, if possible, rather than going to work in a chemical factory (as I had thought for years after I enrolled in chemistry, thinking of my high school professor of chemical plants). In 1968 Volpi had brought with him from Rome two young assistant professors, Vincenzo Aquilanti and Giorgio Liuti, a young research fellow (Franco Vecchiocattivi), and a technician (Emilio Luzzatti) (many years later also Roberto Candori, who came from another group, joined Volpi’s group). I was inspired to do my Master’s thesis with Aquilanti, who had just setup an ion-atom crossed beam machine. This was my first best choice of my scientific life! 4569




research supervisor, Stephanie with me, and wonderful geographical location. (Everytime I was leaving the lab in building 70A at LBL to go to the computer center or the cafeteria for lunch I was stunned by the bay view from the hill, with San Francisco and the Golden Gate in the background. I still have a beautiful photograph of the view at night time from that location hanging on the wall of my office in Perugia.) Yuan put me to work on two projects with Chris Becker, a fourth year, intelligent and hard working graduate student: (a) determination of rare gas−halogen atom interatomic potentials via elastic differential cross section measurements and (b) Li +HF and Li+HCl reactive scattering. I owe a lot to Chris, who introduced me to both elastic and reactive scattering. Our experiments went very well, and numerous papers were published: We determined the potential for F−Xe, Kr, Ar, Ne, and Cl−Xe and enjoyed the collaboration with Bill Lester on quantum close-coupling calculations for F(2P3/2,1/2)-rare gas (1S0) scattering. Later on, before returning to Italy, I extended these studies also to Br(2P) and I(2P) + rare gases with the collaboration of Randy Sparks (a graduate student who had built a state-of-the-art 35″ crossed molecular beams (CMB) machine that we used for the Br and I atom experiments) and Professor Guozhong He, who in 1979 was one of the first Chinese scientists to come to Berkeley (from Dalian) and with whom I had the pleasure to work. Again, who would have thought that more than 20 years later I would have visited him in Dalian, where he had become a member of the Chinese Academy of Sciences and had pushed through the 1980s and 1990s for the great development of Molecular Reaction Dynamics in China. Randy was, together with Chris, one of the first good friends we made in Berkeley. He knew not only how to build a CMB machine but also how to repair our old ’69 Chevy when it stopped running. Randy is one of the people I owe the most to, given the fact that once I returned to Italy I could build a CMB machine that worked on the first try (he had learned all the tricks from Yuan!). Randy is the only Berkeley friend who came to the reception of our wedding in L.A. on August 26, 1982 while he was an assistant professor at Caltech. Incidentally, there was only one other scientist at our wedding, who drove over from Caltech, where at that moment he was spending a research period with Aron Kuppermann: Antonio Laganà! The Li+HF and Li+HCl projects were central for my education in reactive scattering, and we worked very hard on them. Peter Tiedemann (a postdoc from Brazil) was taking good care of the Tantalum oven for the Li beam (that Jim Valentini had built before leaving Berkeley). We also worked overnight during data collection. Unfortunately, the part of the experiment with vibrationally excited HF didn’t work because the lowest few HF rotational lines that we obtained from the home-built (by Jim and Chris) HF chemical laser had a too weak intensity to excite the HF molecules in the beam that were just cooled to the lowest few rotational levels following the supersonic expansion. I did most of the data analysis (which also included the derivation of the Li+HF and HCl intermolecular potentials) and the paper writing while Chris was already at MIT as postdoc and Peter was back in Brazil. Those results represented for theoreticians the reference data for a truly A+BC reaction for about 20 years, until Jürgen Loesch in Bielefeld greatly extended the investigation of the Li +HF reaction down to the threshold. By the way, the Berkeley experimental work on Li+HF kept my colleague Antonio Laganà, his student Stefano Crocchianti (now research

coupling the technique of crossed atomic and ion beams with spectroscopic emission detection led to the discovery of phenomena of polarization and interference in atomic and molecular collisions. I thus published my first papers, in which pronounced oscillatory structures in the velocity dependence of integral inelastic cross sections for emission also from specific magnetic sublevels were reported. In 1975, together with Aquilanti, I attended my first International Symposium on Molecular Beams in Cannes (the fifth in the series started by Marcel Devienne); I remember meeting Jörg Reuss on that occasion. I could not anticipate at that time that one day (25 years later) I would become the Scientific Secretary of that Symposium, succeeding in the role that Reuss, and later on Udo Buck, held for many years.

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BERKELEY DAYS In 1977, after three years of active research in Perugia, it was time for me to have some experience abroad. This was the tradition in the Rome school, where Volpi and his group had originated. I had heard about Volpi being a postdoc with Kistiakowsky at Harvard in the late 1950s, when also Bruce Mahan, Dudley Herschbach, and Bill Klemperer were there and Peter Toennies was close by at Brown. Then, I had heard about Aquilanti in Harvard with Dudley Herschbach and of Giorgio Liuti at Raenssler Polytechnic Institute, Troy, New York with Harteck and then at Goddard Space Flight Center for many years. So, I was very eager to do my experience abroad and open up my eyes to the world. Aquilanti suggested I go to work for Yuan T. Lee, whom he knew since they were both postdocs with Herschbach at Harvard and whom he respected and greatly admired. I had heard a lot about Yuan Lee’s work while he was in Harvard and then in Chicago (where Franco Vecchiocattivi from Volpi’s group had spent a research period in 1974). Yuan Lee had moved to Berkeley, where he had set up an impressive operation. Enzo talked to him about a possible postdoc period of mine in Berkeley. So, when in the spring 1977 I was awarded a one-year fellowship from the Italian National Research Council to do research abroad, I was thrilled about the opportunity to go to Berkeley, also considering that Stephanie was from California: This was my second best choice of my scientific life. Stephanie and I left Perugia on August 1, 1977 and ended up staying in Berkeley until the end of April 1980 (since I could also use my Italian fellowship I had in Perugia to do research abroad, I could continue my postdoc for more than one year). Because the Italian lira was rather weak compared with the U.S. Dollar (or maybe the Italian fellowships were rather modest), Yuan Lee offered me a generous monthly allowance toward living expenses so that I could work without worries. With Stephanie we first lived on Fulton Street and then on Haste Street, always near Shattuck Avenue and the campus. She was doing art and worked part-time for a long period as a secretary (much appreciated for her ability to type from headphone recordings) at the Natural Land and Water Reserves System of UC Berkeley (one of her colleagues there, Jeff Kennedy, and his wife, Judy, have been wonderful friends and kind hosts on many occasions as well as most welcome visitors to Italy, which they love). I was spending a lot of time in the lab, but I occasionally had the opportunity to attend great parties of artists in Berkeley and San Francisco, thanks to Stephanie’s connections. It was the most exciting time of my life: incredible research opportunities at UC Berkeley and Lawrence Berkeley Lab, a wonderful and exciting research group, a world leading, creative 4570




then Matt (with his mate at the time), Dan (with Ellen, just married), and later on Chris and several others. In 1979 Yuan organized an exciting Dynamics of Molecular Collisions Conference in Asilomar, and on that occasion I got to know most of the famous people in the field, including some of the former students/postdocs of Yuan that I had heard about, such as Jim Parson, Jim Farrar, Peter Siska, Dan Auerbach, and Cheuck Ng. (I have a memorable photograph in my office of Yuan with all of his students and postdocs at the meeting, including meSteve was missing because he took the picture, if I well recall!and his secretary at the time, Ann Weigthman). The stimulating interaction and discussions with all of these scientists (students, postdocs and visitors) while in Berkeley strengthened my confidence for future projects once back in Italy.

associate in Perugia), and others of his collaborators busy for quite a long time from the theoretical point of view (both with QCT and quantum scattering calculations, which are very hard for this truly A+BC reaction). The JCP (1980) paper is highly cited (about 150), but Antonio keeps joking that most of those citations are from him! After Li+HF and HCl I fell in love with reactive scattering, and so during my second year in Berkeley Yuan put me to work with Rick Buss and Steve Sibener on reactive scattering of oxygen atoms (with benzene, toluene, methane, molecular hydrogen; we also tried acetylene and ethylene, but these were done much better by Anne-Marie Schmoltner about 10 years later). I tremendously enjoyed working with Steve and Rick. I learned a lot more about reactive scattering working with them on those exciting projects (postdoc Tomohiko Hirooka was also involved in some projects and later on also the new student Bob Baseman). In particular, Steve had built a “magic” radio frequency supersonic oxygen atom beam source, whose capabilities I perhaps did not fully appreciate at that time. I never thought that one day that kind of source would have become the “battle horse” for most of my reactive scattering experiments, after I discovered in the early 1990s that you could use it not only for generating oxygen atoms but also for a variety of atomic (N, C, Cl, S) and molecular (OH, CN, C2) radicals. With Steve we established a life-long friendship with reciprocal visits (also with families) to Chicago and Perugia. I owe a lot to Steve, whom I greatly admire, also for his ability of being a talented speaker. Another good friend in Berkeley was Matt Vernon, who arrived to do graduate school with Yuan shortly after we arrived in Berkeley. Although we never worked together, we became very good friends (we exchanged visits, also with families, several times after the Berkeley days). During the period in Berkeley I was exposed to an incredibly exciting atmosphere, which allowed me to learn the subtleties of crossed beam elastic and reactive scattering experiments and gave me the wonderful opportunity to meet and interact with many future successful scientists, who also became good friends: besides Chris Becker, Steve Sibener, Rick Buss, Randy Sparks, and Matt Vernon also Carl Hayden, Scott Anderson, Carol Kahler, Marta Kowalczyk, Kosuke Shobatake, Tomohiko Hirooka, Bob Baseman, Jim Valentini, Peter Tiedemann, Sylvia Ceyer, Francis Houle, Doug Krajnovich, Peter Schultz, Aasman Sudbo, Sandy Bustamente, Lee Carlson, and Dan Neumark (who arrived the second year I was there) as well as several Europeans who were postdocs at that time in Yuan Lee’s group: Dieter Gerlich (from Freiburg) and Friedrich Huisken (from Goettingen) and visitors such as Manfred Faubel (from Goettingen) and Anna Giardini (from RomeI already knew her because she had been one of the first students of Volpi in Rome). My wonderful friendship with Dieter, Friedrich, and Manfred, three impressive scientists, goes back to those exciting days. One of the memorable things from the Berkeley days are the two annual group dinner parties that Matt Vernon cooked for all of Lee’s group members (and their partners) that I attended, one at Lee Carlson’s house in Livermore and the other at his home in Berkeley. On both occasions I was the official photographer of the event, and I delight looking at those pictures once in a while (Matt had renowned French chef capabilities, having taken one month of French cooking classes at La Varenne in Paris). It has always been enjoyable to receive and reciprocate visits with many of the friends (and families) of the Berkeley times. Steve was the first to visit (with Don Levy),

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BACK TO PERUGIA: THE 30″ MACHINE At the end of April 1980 we were back in Perugia, where Professor Volpi and his assistants had decided to support me in setting up a Crossed Molecular Beams (CMB) apparatus. I spent six months in a large empty room (that would then become my laboratory) equipped with only a drawing table to draw a 30″ Crossed Molecular Beams machine with a rotatable mass spectrometric detector. I think this was the very first 30″ machine created (I only knew of 20″, 25″, and 35″ machines) (30″ is the diameter of the special ball bearing supporting the rotating chamber of the detector). In particular, it was the first (and only) one with the main vacuum chamber made of aluminum alloy. Because we were on the third floor of a building, perhaps stainless steel would have been too heavy, but what played an important role was the fact that near Perugia (at 25 km, on the shores of Lake Trasimeno) there was a large factory conveniently located with expertise in Al-alloy welding. Of course, all the rest of the machine was made of stainlesssteel. It came out as an excellent job: The main chamber pumped down to 8 × 10−8 Torr on the first try. It was an exciting time to build a CMB machine (a lot of determination and perseverance is needed, i.e., you have to know in detail how the final product should look). But we did not have all the money necessary at once, so it took a bit longer than it would have otherwise. Here I want to thank several people who contributed to that endeavor: Besides the boundless support of Professor Volpi, the encouragement also of Aquilanti, Liuti, and Vecchiocattivi, and some expert advice from Emilio Luzzatti, I benefitted in particular from the enthusiasm and collaboration of two people in the chemistry department: Giovanni Nicoziani, an excellent technician in the machine shop (who on several occasions worked for me also on weekends) and made all the small parts needed, and Mario Bazzurri, the electronics technician in the group who helped me with the electrical parts and in assembling various items. When Mario retired (at a very early age), luckily another electronics technician came onto the scene, Giampiero Vincenti, from another institute next door, who also now that he’s retired continues to help in all the electronic problems that we may encounter. He is really a magician of radio frequencies and electronic circuits, able to solve almost any problem; he has been, and still is, always available. From my point of view, I appreciate his invaluable contribution and consider him a wonderful and generous friend. In the machine shop Giovanni continued to be invaluable until his retirement (in 2000)very professional, a great friend. Afterward, his important role has 4571




several prominent figures, such as Millard Alexander, Jörg Reuss, Udo Buck, Fred McCourt, and Ken Janda, and to interact with many others on this topic, such as Peter Toennies, Manfred Faubel, Friedrick Huisken, Klaas Bergman, Bill Miller, Giacinto Scoles, John Fenn, Nadine Halberstadt, Alberto Beswick, Ad van der Avoird, Jeremy Hutson, Roger Miller, Davide Bassi, and Franco Gianturco. At that time, during visits at Berkeley or during conferences, I was also meeting the next generation of Yuan Lee’s students, such as Arthur Suits, Floyd Davis, Laurie Butler, Paul Weiss, Anne-Marie Schmoltner, Tim Minton, Alec Wodtke, Albert Stolow, John Hepburn, Mitchio Okumura, Bob Continetti, and others, who also became good friends and a source of inspiration. During that period I enjoyed collaborating on some systems with colleagues in the Perugia group, Fernando Pirani and Franco Vecchiocattivi, two experts on intermolecular forces, who were measuring in another molecular beam apparatus absolute integral cross sections as a function of velocity, a quantity complementary to the differential cross section. This permitted us, often within a multiproperty analysis also of transport properties and second virial coefficients, to provide very reliable intermolecular potentials for systems such as, for instance, Ne−Ar, Ne−N2, and Ne−O2 (with the largest amount of information coming from the new high-resolution differential cross section data). In particular, many years later I was very happy to see that Fernando Pirani, the true expert in the Perugia group in intermolecular forces and still very active, together with his long-standing collaborator David Cappelletti used my high-resolution elastic scattering data on Ne−Xe, Ne− Kr, Ne−Ar, and Ne−Ne to show that his “Improved LennardJones potential” can reproduce very accurately even the most sophisticated scattering data. The Improved Lennard-Jones potential, with only slightly more than just the two typical LJ parameters, represents a very simple and accurate description of the intermolecular potential, without resorting to multiparameter potential forms (See: Beyond the Lennard-Jones Model: A Simple and Accurate Potential Function Probed by High-Resolution Scattering Data Useful for Molecular Dynamics Simulations. Pirani, Brizi, Roncaratti, Casavecchia, Cappelletti, Vecchiocattivi, PCCP Vol. 10, pp 5489−5503 (2008), Perspective, cover). We published numerous papers on intermolecular forces, and I gave numerous invited talks, but, in particular, I was very pleased to be invited to speak on this topic at the XVII ICPEAC in Brisbane in 1991. Although I continued to publish some papers up to the mid-1990s in collaboration with Fred McCourt (Waterloo) and Ken Janda (Irvine), I had stopped experiments on elastic scattering in the late 1980s because I wanted to move to my (and Volpi’s) initial goal of studying reaction dynamics.

been successfully taken over by his son, Andrea, who, as his father (from whom he has learned a lot), loves to make precision mechanical parts and contribute to the success of experiments. Again, I have been lucky to have encountered on my way Giovanni and Andrea (incidentally, Giovanni Nicoziani, before becoming a university employee, was initially hired on research money in 1968 by Volpi when he moved to Perugia to set up a molecular beam laboratory). Together with Luciana Di Giacinto, my first undergraduate student, we completed the setup of the machine and did a first test by measuring the elastic differential cross section for Ar−Kr (we were happy to observe two well-resolved rainbow oscillations with small error bars and reproduce them with a literature potential). We also implemented the pseudorandom time-of-flight system. (Thank you, Friedrich (Huisken) and Udo (Buck), for the wonderful 4×127 pseudorandom disks! And thank you, Manfred (Faubel), for your assistance with your TOF module!) Antonio Laganà, who had returned from his postdoc with Jonathan Connor, was a reassurance to me in the implementation of scattering programs in the new department computers and for all computational help I needed. Antonio has always been a generous supporter of my scientific work among his Italian computational/theoretical colleagues on many occasions, and this has helped me to find my way through the physical chemistry academic community in Italy. In the first low-resolution arrangement we studied the Ar-NO system (Anisotropic Intermolecular Potentials for NO-Ar and NO-Kr from Total Differential Cross Section Measurements. Casavecchia, Laganà, and Volpi, CPL 1984). After this initial work, although I wanted to study reaction dynamics, I decided to first look at some unsettled issues in elastic scattering and intermolecular potentials, a theme that had reached its maturity by the 1980s but that was still timely and of considerable interest in the scientific community. This required arranging the CMB machine in a high-resolution setup. This decision was a good one because high-resolution elastic scattering is very educational and teaches one to be accurate and quantitative and to obtain a detailed control of your CMB machine. People appreciate seeing differential cross sections with a lot of quantum oscillations (closely spaced) with small error bars. A good business card for your newly built machine!

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ELASTIC SCATTERING IN PERUGIA We then started with elastic scattering experiments and tried to give a contribution to some unsettled issues on the rare gas− rare gas pair potentials (notably the Ne-heavier rare gas series) and some atom−diatom systems, such as He and Ne interacting with simple diatomic molecules. With my second undergraduate and then first Ph.D. student, Laura Beneventi, in 1984 we implemented a high (0.5°) angular resolution of the detector and began with high-resolution experiments on the determination of intermolecular forces via differential cross section measurements for rare gas−rare gas and rare gas− diatom systems. In these experiments all quantum diffraction oscillations (having about one degree spacing) superimposed on the rainbow structure were fully resolved for the first time on challenging systems such as Ne−Ar, Kr, Xe, O2, N2, NO, and Cl2 and clearly separated from the symmetry oscillations in Ne−Ne (this was achieved by detecting both 20Ne and 22Ne). We were using supersonic beams with 0.4° angular divergence and very small velocity spread. This initial work opened the door for me to the club of the leading scattering people and I got to know and collaborate on some of the systems with

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REACTIVE SCATTERING IN PERUGIA In the late 1980s I modified the CMB apparatus for reactive scattering, and with Volpi and Ph.D. student Laura Beneventi (now a chemist at ARPA, the Umbria regional center for environment) I started a broad research program in reaction dynamics. At that time (1988) my current, long-standing collaborator, Nadia Balucani, joined the group, first as an undergraduate, then as my second graduate student, and afterward as a Research Associate. With Laura and Nadia initially the focus was on reactions of O(1D) with molecules of atmospheric interest (HCl, HBr, HI, CH3I, CF3Br, H2S, H2). This work started, to some extent, to establish my reputation in 4572




the field. At that time I better got to know the international community active in molecular beam scattering and reaction dynamics/kinetics: Roger Grice, Chris Whitehead, Ian Smith, Ian Sims, John Simons, Mark Brouard, Claire Vallance, Gus Hancock, Andrew Orr-Ewing, Mike Ashfold, David Clary, David Manolopoulos, Mark Child, Ken McKendrick, Ben Whitaker, Mike Pilling, Paul Seakins, David Chandler, Paul Houston, Jim Sloan, Peter Bernath, Giacinto Scoles, Roger Miller, Dick Bernstein, Dick Zare, Bill Miller, Brad Moore, Bill Klemperer, Paul Dagdigian, Curt Wittig, Hanna Reisler, Dudley Herschbach, John Polanyi, Aron Kuppermann, Ahmed Zewail, Rudy Marcus, Kopin Liu, Jim Lin, David Nesbitt, Carl Lineberger, Steve Leone, Ravi Ravishankara, Paul Wine, Joel Bowman, Don Truhlar, George Schatz, Larry Harding, Al Wagner, Fleming Crim, Craig Taatjes, David Osborne, Musa Ahmed, Ralf Kaiser, Bill Hase, George Flynn, Marsha Lester, Gil Nathanson, Rich Saykally, Anne McCoy, Roger Anderson, Jingsong Zhang, Rafi Levine, Ron Naaman, Benny Gerber, Toshi Suzuki, Toshio Kasai, Hans ter Meulen, Steven Stolte, David Parker, Gerard Meijer, Marc van Hemert, Klaas Bergman, Peter Toennies, Jürgen Troe, Friedrich Temps, Peter Botschwina, Karl Welge, Ludger Schnieder, Eckart Wrede, Peter Andresen, Jürgen Loesch, Joachim Werner, Jürgen Wolfrum, Stephan Schlemmer, Tilmann Märk, Zdenek Herman, Theo Kitsopoulos, Angel Gonzáles Ureña, Javier Aoiz, Luis Bañares, Gerardo Delgado Barrio, Pablo Villareal, Antonio Aguilar, Miguel Gonzáles, Michel Costes, Christian Naulin, Jean-Claude Rayez, Laurent Bonnet, the Orsay and Saclay community in the field (Roger Campargue, Odile Dutuit, Christian Alcaraz, Paul-Marie Guyon, Benoit̂ Soep, Jean-Michel Mestdagh, Jean-Paul Visticot, Raymond Vetter, and others), Martin Quack, Tom Rizzo, Frederick Merkt, John Maier, and others. During the 1990s I had the opportunity to make a series of significant contributions in the field of chemical reaction dynamics. In 1992 I developed a continuous supersonic beam of OH radicals (using the basic Sibener and Lee design of the radio frequency discharge source that was used in Berkeley in the late 1970s and 1980s for oxygen atoms). Together with Ph.D. students Nadia Balucani (now Associate Professor in Perugia) and Michele Alagia (now researcher at the National Research Council (CNR) in Rome and Elettra Synchrotron in Trieste) and postdoc Domenico Stranges (now Associate Professor at University of Rome La Sapienza), we undertook the first truly successful reactive scattering studies of OH by investigating the benchmark reactions OH+D2 and OH+CO, which are of fundamental importance (prototypical four-atom reactions) and of interest in combustion, atmosphere, and astrochemistry. The results stimulated synergistic theoretical work beyond the three-atom reactions in several laboratories (Schatz, Clary, Werner). The papers on OH+D2 (JCP 1993, CP 1996 with theorists Clary and Werner) and OH+CO (JCP 1993) (Schatz did separately QCT calculations on this system simulating our experimental conditions) are highly quoted. In 1995, also with the new Ph.D. student Laura Cartechini (now CNR researcher in Perugia), we performed the first study in crossed beams of the prototype three-atom reaction Cl+H2 in synergy with frontier theoretical work by Don Truhlar (exact QM scattering calculations on an ab initio ClH2 PES and QCT calculations by Javier Aoiz and Luis Bañares) (Science 1996). The above cutting edge (for the time) studies on prototypical three-atom and four-atom reactions had thrust me to the forefront and gained me invitations to speak at the most

important conferences (15th International Symposium on Molecular Beams, 1993; Collision Dynamics Conference, 1993; GRC on Molecular Energy Transfer, 1993 and 1995; Stereodynamics Conference, 1994; International Symposium “100 years after Max Bodenstein”, 1995; COMET XV, 1995; 23rd International Symposium on Free Radicals, 1995; IAU Symposium 178 “Molecules in Astrophysics”, 1996; ACS Fall National Meeting, 1996; 14th International Symposium on Gas Kinetics, 1996; IMS International Conference, 1997; Bielefeld International Conference on Stereodynamics, 1997; ECAMP VI, 1998, MOLEC XII, 1998; ACS Spring National Meeting, 1998; Faraday Discussion 1999; 25th International Symposium on Free Radicals, 1999). It was an exciting time also because of the stimulating interplay with theory. I also wrote several review type articles (J. Chem. Soc. Faraday Trans. (1995, Feature Article); Annu. Rev. Phys. Chem. (1999); Acc. Chem. Res. (1999, Cover), and what perhaps is one of the most comprehensive and quoted reviews on CMB reactive scattering [Rep. Prog. Phys. (2000)] (Thank you, Mats (Larsson), for the invitation! I am afraid by now it needs an updating.) In the 1980s and 1990s I was involved in the Local Organizing Committee of many of the International Meetings that Enzo Aquilanti organized in Perugia and Assisi over the years, and I was certainly ready to be the main organizer myself. I organized as Chairman three international conferences: COMET XVI - International Conference on Molecular Energy Transfer in 1999 (together with Antonio Laganà as cochair) and the XXVI International Symposium on Free Radicals in 2001, both in Assisi, and 14th SASP - Symposium on Atomic and Surface Physics in 2004 on the Italian Alps at La Thuile. All three meetings turned out to be very successful. In particular, all my skier friends from all over the world, including Leon Phillips from New Zealand, were at La Thuile for SASP to enjoy a sunny week of memorable skiing! During the above period I enjoyed and learned a lot from the community of the GRC, DMC, ACS, COMET, MOLEC, and FRS meetings. In particular, I had the honor to enter into the community of the Free Radicals Symposium (FRS) (thank you, Hans (ter Meulen)), and I got to know and interact with distinguished scientists like Alan Carrington, John Brown, Terry Miller, Mats Larsson, Anthony Merer, Bob Curl, YuanPern Lee, and many others. It is a great honor to continue to be part of the restricted International Advisory Committee of this historical Symposium series. It has been such a stimulating community since the first meeting I attended in Victoria (Vancouver Island) in 1995. In 1999 I was awarded as Coordinator a 4 year (2000−2004) EC RTN (Research Training Network) on “Reaction Dynamics” (FP5), which involved eight world-leading European teams (four theoretical and four experimental) that turned out to be very successful (see PCCP 2004, Vol. 6, Issue 21, Cover). It was really exciting to work with Oxford (two teams: Mark Brouard, David Manolopoulos), Nijmegen (Hans ter Meulen), Bielefeld (Hans-Jürgen Loesch), Stuttgart (HansJoachim Werner), Munich (Uwe Manthe), and Madrid (Javier Aoiz). At the various Network annual meetings it was most stimulating to have as Invited speakers people such as Kopin Liu, Xueming Yang, Floyd Davis, Jean-Michel Launay, and David Clary among others. In the second half of the 1990s we also developed the first continuous supersonic beams of nitrogen atoms and for the first time undertook their reactive scattering, a long-standing challenge in the field that was tackled in several laboratories 4573




a long-lasting friendship with Tim and Donna that has seen me in Montana at least two times, the second time (in 2005) for a fabulous week vacation involving both of our families, with memorable excursions in Montana and Wyoming, including Yellowstone. Tim and Donna were also in Perugia recently, and with Stephanie and other visitors (Joel Bowman, David Chandler, and their wives) we showed them some special sights of Umbria (Monti Sibillini, Norcia, and Castelluccio) that I believe reminded Tim and Donna (to some extent) of Montana. It is always good to see Tim and discuss science and life with him. Other particularly fruitful and enjoyable collaborations have been with Michel Costes, Christian Naulin, and Astrid Bergeat on C atom reactions. I have always enjoyed visiting Michel in Bordeaux and also to attend the several meetings that he has so well organized in Arcachon (what a memory of the good wines and excellent oysters!). Merci beaucoup, Michel! You are a good friend. Another fruitful and enjoyable collaboration has also been with the Rennes group (Sébastien Le Picard, André Canosa, Ian Sims). I have always enjoyed to be in Rennes and St. Jacût de la Mer, within the several joint small grants (Galileo, PICS) with Sébastien on Astrophysical Chemistry projects. Sébastien (and later on also EU postdoc Kevin Hickson and visitor from Rennes Coralie Berteloite) played a critical role in optimizing our LIF (LaserInduced Fluorescence) apparatus in Perugia. It was exciting to combine dynamics and low-temperature kinetics (as well as theory, with Marzio Rosi from Perugia) on sulfur S(1D) reactions with saturated and unsaturated hydrocarbons. But I cannot forget the extensive collaboration that we had with Javier Aoiz and Luis Bañares and their colleagues in Madrid, also within a two year Acciones Integradas grant. I met Javier at an incredible number of meetingsalways good to see him and also to talk to him about science and life. During the 1990s and early 2000s, as I have summarized, our group focused mainly on simple, prototypical three-atom and four-atom reactions, for which the interaction between experiment and theory is particularly strong. I undoubtedly enjoyed it immensely and learned a lot from all the collaboration with many theorist friends, but as a chemist, feeling that the three-atom and four-atom reactive scattering problem was becoming (arguably) a solved problem, I wanted to move to more complex (polyatomic) elementary reactions, which, besides being of fundamental interest, are of relevance in areas of practical importance, such as atmospheric chemistry, combustion chemistry, and astrochemistry. The Perugia group has often been involved in EC Networks in astrochemistry as well as, up to the present days, in COST Actions in both astrochemistry and combustion chemistry, thanks to the hyperactivity of Antonio Laganà at the EC level and of the deep involvement of Nadia Balucani. Particularly interesting are the reactions of atomic oxygen with unsaturated hydrocarbons, of much relevance in combustion. Chemists started to investigate the kinetics of these reactions from the 1950s to the 1960s, yet at the beginning of the year 2000 the primary products and the branching ratios of these elementary multichannel nonadiabatic reactions, such as O(3P)+ethylene, propene, and so on, which are characterized also by the possibility of intersystem crossing (ISC) between triplet and singlet PESs, were out of reach of detailed dynamical investigations. Pioneering CMB work had been done in Roger Grice’s and especially Yuan Lee’s laboratories in the 1980s. The only detection technique capable, in principle, of interrogating on the same footing all possible product channels

without much success in the 1970s. The study of the prototype insertion reaction N(2D)+D2 prompted synergistic theoretical work (PES by Harding at Argonne and Rabitz at Princeton and dynamical calculations by Schatz at Northwestern) and was published in a joint paper (JPC A, 1999). The reactions of N(2D) with the simplest unsaturated hydrocarbons, acetylene (JACS 2000, with theory from Takayanagi) and ethylene (JPC A 2000), of interest in the atmosphere of Titan, were also investigated. Further experiments on N(2D)+H2 prompted the group of Launay (Rennes) to carry out the first QM scattering calculations on an insertion reaction (the joint work was published, with QCT calculations by Aoiz and Bañares, in PRL (2002)). In 1999, within an EC TMR (Training and Mobility of Researchers) network on astrophysical chemistry (led by Ian Smith and Ian Sims), with new graduate student Giovanni Capozza (now manager at Efeso Consulting, Milan), we developed continuous supersonic beams of C(3P,1D) and undertook, also with postdoc Astrid Bergeat (now at the University of Bordeaux - CNRS), the investigation of important reactions of C(3P) with unsaturated hydrocarbons (C2H2, C2H4) of interest in interstellar chemistry, adding, over the years, some important additional information to the pioneer work of Ralf Kaiser, Arthur Suits, and Yuan Lee on these systems. Besides a paper in Faraday Discuss. Vol. 119 in 2001, joint papers with Michel Costes and Christian Naulin (Bordeaux) were published in JCP 2002, JCP 2003, and Faraday Discuss. Vol. 133 (2006), and an article on a combined theoretical and experimental study of the most important neutral interstellar reaction, C(3P)+C2H2, was also published with Ian Smith, Ian Sims, and David Clary in JPC A (2002, Feature Article, cover). The latest conclusive developments on this reaction, reporting branching ratios in a wide energy range and comparisons with the latest theoretical work, appeared in JPC A (2008), where the astrophysical implications are discussed (Michel and Ralf added some further detail later on). In 2000, following the availability of a beam of C(1D), it also became possible to study, after O(1D)+H2 (JCP 1998) and N(2D)+H2 (PRL 2002), another benchmark insertion reaction, C(1D)+H2 (CPL 2000), which also triggered synergistic theoretical work (PES and QM calculations by Launay and Honvault and QCT by Aoiz and Bañares) leading to several joint publications (C(1D)+H2: PCCP 2004, Mol. Phys. 2010; C(1D)+D2: JCP 2005). A review on insertion reactions was published (Int. Rev. Phys. Chem. (2006)). The work on Cl +H2(D2) continued to stimulate state-of-the-art theoretical work: H.-J. Werner with postdoc Gabriella Capecchi (a former Ph.D. student of Aquilanti) calculated a new PES including spin−orbit interaction, and M. Alexander performed QM scattering calculations on three-state coupled PESs, and this led to joint publications (PRL 2003, PCCP 2004). In 1996 I also started a joint project with Tim Minton (Bozeman, Montana) on gas−liquid surface interactions. I had met Tim for the first time at the DMC meeting in Wheeling, WV in 1987. Then we got to know each other much better at the photochemistry meeting organized by Paul Wine in 1992 in Atlanta, which is when we planned a joint experiment. Tim came to Perugia with a student for three months in October 1996 and we studied the reactive scattering of O and Cl atoms with a liquid hydrocarbon surface (squalane) in the thermal energy regime, something complementary to the hyperthermal scattering work that Tim was doing in his lab in Montana. Joint papers in Faraday Discuss. Vol. 108 (1997) and JCP (2001) received numerous citations. That joint project certainly started 4574




of these reactions was recognized to be a “universal” type of technique such as mass spectrometry in a CMB setup. Unfortunately, mass spectrometry in the usual “hard” electron ionization setting is plagued, for these purposes, by the “dissociative ionization” problem. In fact, Yuan Lee in the second half of the 1990s conceived and prompted the implementation of the soft photoionization mass spectrometric detection in dedicated CMB machines, exploiting the brightness of third-generation synchrotrons, first at the ALS in Berkeley and then at the NSRRC in Hsinchu (Taiwan).

these developments opened up new exciting avenues of research in reaction dynamics and permitted us to bridge the gap between dynamics and modern kinetics studies (with soft photoionization by synchrotron radiation) of elementary gas phase reactions. From this progress I was invited to present 25 invited talks over about ten years at numerous international conferences, and in 2008 I was most pleased and honored to be awarded the Polanyi Medal from the Royal Society of Chemistry-Gas Kinetics Group on occasion of the 20th International Symposium on Gas Kinetics in Manchester, U.K. (When I read the list of previous Polanyi medallists I was extremely intimidated!) Something that I am fairly proud of is the chapter I had the opportunity to write in 2010, together with the outstanding scientists and very good friends Kopin Liu and Xueming Yang, for Tutorials in Molecular Reaction Dynamics (edited by Mark Brouard and Claire Vallance) on reactive scattering. Thank you, Mark! In June 2012, with a goal of trying to bridge the gap between gas, condensed phase, and interfaces, I was honored to organize and chair Faraday Discussion 157 “Molecular Reaction Dynamics in Gases, Liquids and Interfaces”, which was held in Assisi (my favorite site for conferences) and turned out to be very interesting and stimulating. Antonio Laganà (with Ernesto Garcia) on this occasion presented a significant, theoretical/ experimental joint paper with us on the reaction OH+CO, in which his theoretical predictions were compared with our old CMB results. The conclusion was that more work is still needed to better understand the dynamics of this fundamental reaction. About ten years ago our group also set up a new molecular beam-laser instrument with the collaboration of a laser expert from the department, colleague Paolo Foggi. We also received the initial contribution of EC postdoc Paul Sharkey (a former Ph.D. student of Ian Smith in Birmingham), postdoc Alessandra Paladini (a former Ph.D. student of Anna Giardini in Rome, now researcher at CNR-Rome), and Master’s student Giuseppe Restani for LIF measurements to characterize the internal (ro-vibrational) quantum state distributions of the molecular radicals (such as OH, C2, and CN) contained in the beams of reactants employed in reaction dynamics studies with the universal CMB machine (Planet. Space Sci. 2009, Mol. Phys. 2010). This LIF work was mainly carried out by postdoc Francesca Leonori and EC postdoc Kevin Hickson (another former Ph.D. student of Ian Smith in Birmingham, now researcher at the University of Bordeaux-CNRS), with important contributions from Sébastien Le Picard from Rennes during his frequent visits to Perugia. Recently, also the REMPI/ TOF (Resonance-Enhance-Multi-Photon-Ionization/Time-ofFlight) detection technique has been implemented on the same apparatus with some help from visitor Coralie Berteloite (from the group in Rennes of Le Picard and Sims). Over the past decade we have mainly focused on the dynamics of multichannel nonadiabatic reactions, such as those of ground state oxygen atoms O(3P) with unsaturated hydrocarbons (acetylene, propyne, ethylene, propene, allene, and very recently also 1-butene), which are combustion relevant. By exploiting soft electron ionization it has been possible, 50 years after the pioneering kinetics work on these reactions of Cvetanović (and others) and the pioneering CMB work of Lee’s group in the 1980s, to unambiguously identify all the primary reaction products and determine their branching ratios as a function of collision energy. After the initial studies on O(3P)+C2H2 and C2H4, these experiments for the most part

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SOFT ELECTRON IONIZATION: A NEW TWIST IN REACTIVE SCATTERING In 2002−2003, in order to overcome the main complication and limitation in CMB reactive scattering experiments on polyatomic multichannel reactions, that is, the dissociative ionization of reactants/products and background gases under “hard” (70−100 eV) electron impact, together with Ph.D. student Giovanni Capozza (later on we were also joined by Ph.D. students Enrico Segoloni and Francesca Leonori and Master’s (and Post Lauream) student Raffaele Petrucci) we successfully implemented, for the first time on a universal CMB apparatus, the “soft” electron−ionization (EI) detection by using low-energy tunable electrons. This turned out to be a new twist in reactive scattering studies, which allowed us a new class of experiments, after 35 years since the invention of the technique (in 1969 at Harvard by future Nobel Laureates D. R. Herschbach and Y. T. Lee). In particular, it proved to be an attractive alternative to soft photoionization by VUV synchrotron radiation, which initially, in the first implementation in Berkeley, proved to be of limited success for reactive scattering studies for sensitivity reasons (now outstanding work has been performed for over 10 years in Taiwan). Two initial studies exemplified the power of this approach: O+C2H2 (JCP 2004) and O+C2H4 (JPC A 2005, Cover). The CMB apparatus was also equipped, for the first time in these instruments, with the possibility of crossing two reactant beams at angles both lower (45°) and larger (135°) than the usual 90°. This permits us to extend the range, on both the low and high sides, of collision energies that can be attained and is of importance for astrochemistry and combustion relevant reactions, respectively. I was very happy to present the first results on soft electron ionization in an invited talk at a Molecular Beam Symposium (the XX, in Lisbon, 2003), dedicated to Yuan T. Lee who could certainly appreciate it. Another little step beyond state-of-the-art at that time has been the first CMB study with continuous beams of a radical− radical reactions [O+allyl (PCCP 2007) and later on O+methyl (PCCP 2011)] with Mimmo Stranges from Rome. Again, the increased sensitivity of the CMB apparatus and the novel soft electron ionization method were the key. Exploiting a supersonic beam of N(2D) atoms in that period we also investigated reactions of great interest in the atmosphere of Titan, such as N(2D)+CH4 (JPC A 2009) and N(2D)+C 2H6 (Faraday Discuss. 2010), with synergistic theoretical work done by colleague Marzio Rosi (University of Perugia) and Dimitrios Skouteris (former postdoc in Perugia with me and Antonio Laganà within the EC Network on Reaction Dynamics, then postdoc with Antonio and now research associate at “Scuola Normale Superiore” in Pisa with Vincenzo Barone). The new work with soft electron ionization and the study of radical+radical reactions gained me some recognition because 4575




whom I certainly met more often at international meetings is Millard Alexander, whom I met for the first time at the DMC meeting in Asilomar back in 1979. At the time I confused him with Paul Dagdigian. I got confused about which one of them was the experimentalist and which was the theoretician! It all started at another DMC meeting (Wheeling, West Virginia, 1987) with inelastic scattering on Ne−N2, for which we agreed that Millard would perform the close-coupling calculations to verify the reliability of our IOSA approximation that we were using to fit our total (elastic+inelastic) differential cross section data for deriving anisotropic potentials. That was my first joint paper with Millard in JCP (1988). Later on, the collaboration also continued on reactive scattering, specifically on Cl+H2, where Millard exhibited all his expertise with QM scattering calculations on spin−orbit coupled PESs calculated by Joachim Werner, the king of potential energy surfaces for small systems including spin−orbit interaction. More recently, with Millard we went back to inelastic scattering with a joint Perspective in Science (2013) triggered by the outstanding work by Michel Costes, Christian Naulin, and their coworkers. Millard, I truly appreciate your friendship over many years and always enjoy talking to you about science as well as about life! I also greatly enjoyed the great skiing together, also with Joachim and many others at La Thuile! As you once said, “We are leading a rich life without being rich,” referring to the extensive traveling and the many gatherings all over the world that we do as scientists. But the scientist who perhaps breaks the record at one time is Giacinto Scoles: He counted that in one year (around the mid1990s) we met six times at six different meetings! Giacinto, I always remember the visit to your lab in Princeton and thank you for both the kind hospitality and the long car ride to the Gordon Conference on Atomic and Molecular Interactions in New Hampshire. At conferences I also very often met George, Joel, Don, David, Joachim, and Javier, among others. On Cl+H2 I found most exciting and illuminating the initial collaboration with Don Truhlar and Javier Aoiz (Science 1996, PCCP 2000). The collaboration with David Clary and Joachim Werner on OH +D2 (CP 1996) was central for a detailed characterization of the reaction dynamics of this prototypical four-atom reaction. On insertion reactions [N(2D)+H2/D2 and C(1D)+H2/D2] we initially collaborated with George Schatz (QCT) and then with J.-M. Launay (quantum) and Javier Aoiz and Luis Bañares (QCT) on a new ab initio PES. When we moved to polyatomic multichannel nonadiabatic reactions, a subject of which George Schatz did the pioneering work on O(3P)+ethylene comparing his results with our experimental results, for extensive QCT calculations on coupled triplet/singlet PESs we resorted to a stimulating collaboration with Joel Bowman (and Bina Fu, now in Dalian) who, with his method of permutationally invariant PESs, could afford global multidimensional triplet/singlet PESs for O(3P)+C2H4 (PNAS 2012, JCP 2012, JPC A 2015). This kind work, as well as the work that very recently we have been doing with Carlo Cavallotti (nonadiabatic statistical calculations on coupled high level ab initio triple/singlet PESs) is really the way to disentangle the detailed dynamics and kinetics of multichannel, combustion relevant, reactions. Finally, I was delighted to attend the conferences organized in honor of the 60th birthday of Don Truhlar (2004) and of Joachim Werner (2010), where I met all at the same time so many theoreticians.

have been carried out with former Ph.D. student and then postdoc Francesca Leonori and with the valuable help of various Master’s students and visitors. For the last two years this research line has been continued with enthusiasm and energy by Ph.D. student Gianmarco Vanuzzo, very recently joined by new Ph.D. student Adriana Caracciolo and various master students. The reactive scattering studies on O(3P)+unsaturated hydrocarbons have often been accompanied by synergistic theoretical investigations, both at the level of ab initio calculations of potential energy surfaces and at the dynamical level (by the QCT surface-hopping (SH) method) and/or statistical (RRKM-Master Equation) calculations, including nonadiabatic effects. This has permitted us to explore the role played by intersystem crossing in these important combustion reactions and to achieve a detailed understanding of the complex reaction mechanisms. Following our initial experimental work of 2005 on O(3P)+ethylene, George Schatz did the first QCT-SH studies on-the-fly on the nonadiabatic dynamics of this prototype reaction. More recently, a fruitful collaboration with Joel Bowman (and his postdoc Bina Fu) on this prototypical multichannel reaction has led to benchmark joint experimental/theoretical papers (PNAS 2012, JCP 2012). Very recently these studies were also extended at high energy (again, with Joel and Bina Fu, now holding a position at DICP in Dalian, JPC A 2015). More recently, the mechanism of the even more complex O(3P)+propene (JPC C 2015) and O(3P)+propyne (this JPC A issue) reactions has also been disentangled by combining the CMB work with high-level ab initio calculations of triplet and singlet PESs and their coupling and statistical calculations with inclusion of intersystem crossing, in collaboration with Carlo Cavallotti (Polytechnic of Milan). New insights into the role of ISC and product identities, such as triplet ethylidene+formaldehyde from O +propene (JPC Letters 2014) and singlet ethylidene+CO from O+propyne (JPC Letters 2016) have been obtained. An overview of the progress made in this area appeared in 2015 in International Reviews in Physical Chemistry. In closing this section, I want to thank the Molecular Beam community, and, in particular Javier Aoiz and Luis Bañares, the organizers of the XXVI International Symposium on Molecular Beams, held in Segovia June 29−July 3, 2015, for the dedication of the 2015 Symposium edition to me and Mike Ashfold, a most distinguished scientist and long-standing friend with whom I have been most honored and pleased to share the recognition.

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SYNERGY BETWEEN EXPERIMENT AND THEORY A particularly strong synergy between experiment and theory characterizes the field of molecular reaction dynamics. This is certainly an area of research where interplay between laboratory experiments and theoretical calculations is most important and often critical, with experiment often leading theory and vice versa. I was fortunate enough and most honored to have collaborated fruitfully over the years, as I have mentioned, with quite a number of distinguished theoreticians, among the best on the scene, who got interested in our experimental work on reaction dynamics (Millard Alexander, Don Thrular, Joachim Werner, David Clary, George Schatz, Javier Aoiz, Luis Bañares, Jean-Michel Launay, Pascal Honvault, Joel Bowman, Antonio Laganà, Marzio Rosi, Dimitrios Skouteris, Carlo Cavallotti). This has been, and still is, very exciting, stimulating, and enlightening. It also resulted in long-standing and much appreciated friendships. I think that the theoretician with 4576




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Perugia. Well, every day that figure was giving me more confidence that “soft electron ionization” would have worked very well. Indeed, once back in Perugia we were ready to try, and admittedly, it worked on the first try, beyond any expectation. That was certainly a big step in my lab, which has determined many of the accomplishments of the last ten years. With the girls growing up and Giulia getting involved in serious studies of the Chinese language at Perugia University (Bachelor’s) and Venice University (Master’s), and with the incredible uprising of science in China at the turn of the millennium, in 2007 we all packed for the Far East to spend two months as Visiting Professor at the Dalian Institute of Chemical Physics with Xeuming Yang, the world star of molecular reaction dynamics, who had set up a most impressive operation in Dalian once he returned to China. I had met Xueming for the first time at a synchrotron meeting in Berkeley in 2000 and then visited him, upon his kind invitation, at IAMS in Taipei. A super exciting experience for all: Giulia took the opportunity by enrolling at a college in downtown Dalian for a two month intensive course of Chinese, while the rest of us very much enjoyed staying in a wonderful accommodation near Xinghai Square where Xueming lives. Thank you again, Xeuming, for arranging everything so perfectly! It was very exciting every day to be in the lab interacting with the impressively intelligent and hard working students of Xueming and in the evening, during the spectacular International Beer Festival in Xinghai Square, to stroll with Stephanie, Elisa, and Xueming through the music and beer expositions: It is there that I learned to drink and appreciate some beer! In Xueming’s lab I had the great opportunity to work on a long-standing problem (the reaction Cl+H2) that I had studied 10 years earlier in Perugia and published in Science with Don Truhlar and Xavier Aoiz. But tackling this prototype system with the powerful H atom Rydberg tagging technique and taking into account also the spin−orbit interaction led to a conclusive experimental/ theoretical paper on the subject that I had the honor to be involved in (again in Science 2008, with Xueming Yang, DongHui Zhang, Millard Alexander, and Joachim Werner). DongHui was also an exquisite host on various occasions. During my stay in Dalian I particularly enjoyed meeting Guozhong He again, an Academician and one of the founding fathers of molecular reaction dynamics in Dalian (and China), with whom, as I have already mentioned, I had the great pleasure to work with in 1979−1980 when I was a postdoc in Berkeley in the group of Yuan Lee. Guozhong sends us the most beautiful New Year’s greeting card “every single year” since the Berkeley days. Thank you, Guozhong! Finally, Stephanie was most impressed by China (her first time), and in Dalian she dedicated herself to photographing the people (the three photography shows she had on China when she returned to Italy were very successful and appreciated). The leader of the Cl+H2 project in Dalian was Xingan Wang, a terrific, very kind, hard-working Ph.D. student of Xueming that I had the great pleasure to meet and work with during those two months. This was the beginning of a wonderful friendship. Xingan was later on a postdoc in my group in Perugia for three months within a European Marie Curie Network on Astrophysical Chemistry, and for the last two years I have been visiting him regularly as a visiting professor during the summer at USTC (University of Science and Technology of China) in Hefei, where a few years ago he became Professor

VISITING PROFESSORSHIPS One of the most wonderful opportunities offered to a scientist is the status of Visiting Professor. This is something that one usually does with his family, and this is what makes it particularly memorable. My first experience was “Professeur Invité” for one month at “Université d’Orsay” in Paris with Odile Dutuit in 1997. The family stayed near le Cirque d’Hiver, at walking distance from Place des Vosges. Every day I was taking the RER to Orsay while Stephanie, Giulia, and Elisa strolled around Paris. Of course on weekends we visited places together like Versailles. This was in September, and Giulia in October started her first year of French in junior high, a language that she also continued to pursue in high school. The second experience was a visiting Miller Professorship in Berkeley for two months with Dan Neumark. Needless to say, it was exciting to be back there (again with the family for half of the time), a place where I had spent almost three years as postdoc 20 years before. Thanks to Dan I was again exposed to the incredible amount of top science being made in the Olympus of physical chemistry and beyond. The Miller status is something I would recommend to everyone, and thanks also to Dan and Ellen, and their superb hospitality, my stay in Berkeley was truly memorable. I very much enjoyed to go almost every day to Café Roma after lunch for a coffee with Dan, Bill Miller, Rich Saykally, Steve Leone, Charles Harris, Paul Alivisatos, and others. At that time I also enjoyed the hospitality of Robert Littlejohn (I stayed at his place for one month), from the Berkeley physics department, a frequent visitor of Perugia, where he collaborates on theory with Enzo Aquilanti. On that occasion I had the pleasure to visit for a seminar David Nesbitt in Boulder (where I returned again, also when I was on my way to Telluride). Thanks David and Ricky for the warm hospitality. On those occasions I went to a party at Carl Linberger’s artistic home and a “cowboy” breakfast on the Rockies with Barney Ellison and paid a visit to Ravi Ravishankara at NOAA. On the way back to Italy I also made a stop to visit the chemistry department at Columbia (thanks, Jim, for organizing the seminar). But another experience that I would also recommend to everyone is the Visiting Erskine Professorship that I had the luck and privilege to enjoy in the summer of 2002 for two months at the University of Canterbury in Christchurch, New Zealand. Needless to say, the four of us packed eight large suitcases (it was winter “Down Under” and we were supposed to also go skiing), and with enthusiasm we headed to New Zealand, with fabulous stops at the Barrier Reef and Sydney. What made the experience unique and off scale was the beauty of the Southern Island and the exquisite, generous, and truly wonderful hosts, Leon and Pam Phillips! Thank you, Leon and Pam, from all of us, forever! So many memorable experiences! Too many to list here, but the trip to the West Coast and the Sounds was undoubtedly the highlight. Giulia and Elisa also loved the brief school experience there. I particularly enjoyed to deliver a course in Molecular Beam Scattering Dynamics to a class of honor students. Something special that occurred at that time is that just outside my office, as I was opening the door, I found hanging on the wall a poster in front of the group of Peter Harland with a striking figure showing the ionization cross section of CO2 as a function of electron energy for the parent ion and all daughter ions! Incredible: I had already commissioned, before leaving Perugia, all the necessary parts to start trying “soft electron ionization” in my CMB apparatus in 4577




friendly dinner with families at the Athenaeum). When I went back for another seminar (a few years later, in January), invited this time by Mitchio Okumura, I was stunned to see at lunch time at the Athenaeum such a famous scientist as Stephen Hawking, who I was told liked to spend winters in warm Southern California. Of the very many conferences I have attended, one remains particularly memorable to me and Stephanie (particularly for the outstanding accommodation): the 2004 Free Radicals Symposium at the Formosa Hotel in Taipei. Thank you, YuanPern!

and has set up a state-of-the-art molecular and laser beam laboratory. We plan to go to USTC also next summer.

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VISITORS AND VISITS The visitors received in Perugia over the years, from one week to a few months, are also wonderful memories. The first visitor I received in my lab for several months was Lev Rusin, from the Academy of Sciences of Moscow. We worked together successfully on NO cluster scattering from He beams. Jörg Reuss was a visiting professor in the Perugia group from Nijmegen in the late 1980s (we combined the Perugia scattering data with the Nijmegen magnetic data for Ne−O2). Dave Chandler came for a short visit in the early 1990s, and afterward he visited us in Perugia with family on several occasions. We have been to Livermore several times, too, including, being invited to the wedding of David’s daughter. One time we also met Mike Ashfoldat David’s home together with the familywho was spending some time with Dave: memorable the jacuzzi under the stars! With Jim Sloan I have exchanged many visits during our joint NATO grant. Stephan Schlemmer came to help us one time. Toshi Suzuki also came to visit for a week after I had been in Okazaki for a wonderful meeting that he organized in 1997. As I have already mentioned, Tim Minton was in Perugia for three months in 1996. Oskar Asvany also came for a visit when he was a student with Ralf Kaiser. I paid several visits to Hanscom AFB near Boston when I had an EOARD grant with Ed Murad, and I was very pleased when Ed came to a meeting that I organized in Assisi and to see the lab (I remember Mike Berman was with him). Leon Phillips (and Pam) came to spend a few months sabbatical in Perugia, and we were delighted to celebrate with them the turn of the millennium in a party at our home. Sébastien Le Picard from Rennes has spent periods of one week or more several times in Perugia. Astrid Bergeat has also been to Perugia several times for different periods after her postdoc time. Wolf Geppert and his student Mathias Hamberg came during two different occasions for several weeks. It was memorable to visit him and Mats Larsson in Stockholm and the storage ring CRYRING at the Manne Siegbahn Laboratory. Vaclav Nevrly from the Czech Republic has also spent two different periods in our group within a COST action on Combustion. I myself visited many laboratories over the years. Besides those that I have already mentioned, I also want to remember most interesting and enjoyable visits (from a few days to a week) to Klaas Bergmann in Kaiserslautern; Udo Buck, Friedrich Huisken, Peter Toennies, and Manfred Faubel in Goettingen; Ken Janda in Irvine; Greg Parker and Mark Keil in Norman, Oklahoma; Bob Gilbert in Sydney; Hans ter Meulen in Nijmegen; Karl Welge in Bielefeld; Dick Bernstein at UCLA; Dick Zare in Stanford; Tim Minton in Bozeman (Montana); Javier Aoiz and Luis Bañares in Madrid; Xueming Yang, Kopin Liu, and Jim Lin at IMS in Taipei; Yuan-Pern Lee and S.-H. Lee in Hsinchu; Mark Brouard in Oxford; Mike Ashfold and Andrew Orr-Ewing in Bristol; Ian Smith and Sue in Cambridge; David Nesbitt in Boulder; Michel Costes in Bordeaux; Martin Quack at ETH-Zurich; John Maier in Basel; and Stephan Schlemmer and Oskar Asvany in Koeln. I want to thank all my hosts on those occasions for the most friendly and generous hospitality. Among the visits to various institutions for seminars I was mostly impressed in the mid-1990s to be at Caltech and visit the laboratories of Ahmed Zewail (thank you, Ahmed, for the

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SOME FINAL CONSIDERATIONS ABOUT SCIENTIFIC RESEARCH IN ITALY TODAY In retrospect, I have been very lucky to have started my scientific career at a propitious time, when Italy was coming out promisingly from the disasters of World War II with a lot of programs and good intentions. The massive university developments in the 1960s, 1970s, and 1980s allowed the blossoming of many good laboratories in many chemistry departments throughout Italy. The Perugia Molecular Beam group, including myself, has benefitted tremendously from that positive derivative. Then, in the 1990s, when the political system entered a crisis of identity (a euphemism for corruption, some incapacity, and lack of sight for the future in scientific research), things started to flatten and shake, transmitting motifs of worry for how the academic system was exhibiting serious difficulties in approaching/adopting the standard of more developed countries. These countries traditionally are very conscious about scientific research and invest a sensible amount of resources in it, both in the enrollment methods of new professors and in the funding extent and procedures as well as in the modernization of the university infrastructures. With the financial crisis of 2008, the Italian university system started to suffer such severe cuts and lack of attention by the political class that today it is choking more and more every year. Suffice it to say that today (actually since about a decade) it would be impossible to build a CMB machine as I was able to do in the 1980s or something of equivalent size in a chemistry department in Italy. This is sad, but with my naive trust that politicians and ruling class would have improved over the years, I could have never imagined in the 1980s to early 1990s that the Italian universities would have instead taken a frightening downhill road in scientific research, that would perhaps jeopardize the future of the country. This poses tremendous challenges to the new generations who will have to face huge difficulties in a historical period in which scientific development accelerates. I only hope that Italy, mindful of its great cultural history, soon will find the awareness and determination to invert the current negative trend. Piergiorgio Casavecchia

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ACKNOWLEDGMENTS

I am much indebted to Enzo Aquilanti and Gian Gualberto Volpi for how they believed in me and their continuous and boundless support over the past 40 years. I also owe much to all the other members of the Perugia Molecular Beam group, in particular, Bruno, Franco, Fernando, Antonio, and Gaia (we all started at about the same time) for the friendly, serene, stimulating, and supportive atmosphere over many years on the same “third floor” and through many scientific and life adventures. But I am also thankful for the cooperation and 4578




friendship of all the other members who joined the Molecular Beam group later on: Simona Cavalli (with Enzo Aquilanti), Stefano Crocchianti (with Antonio Laganà), David Cappelletti (with Fernando Pirani), Stefano Falcinelli (with Franco Vecchiocattivi and Bruno Brunetti), Andrea Lombardi (with Enzo Aquilanti), and especially Nadia Balucani, who has been collaborating with me with enthusiasm for the past 25 years, since her student times. Many thanks to the many undergraduate and graduate students as well as postdocs who have contributed with dedication to the Crossed Molecular Beam science done in Perugia in my group over the past 30 years. I also want to thank the members of the technical and administrative staff of the department who have always tried their best to keep the department going. I thank Dr. Susan Lepri for her generous help in finalizing the Cover Art for publication. Very special thanks go to Yuan T. Lee, a most special, brilliant, inspirational, socially and environmentally conscientious, and sustainability committed scientist that I had the immense honor and luck to work for as postdoc. Stephanie will certainly join me in thanking you, Yuan and Bernice, for your kindness in the various occasions we met (from Berkeley to Taipei to Hawaii). Finally, besides my parents, brother, sister, and my daughters (Giulia has been working for China Radio International in Beijing for three years; Elisa, after her Master’s in marketing, communication, and new media at the University of Bologna, is right now working for LVMH in Milan), I want to thank especially my beloved wife, Stephanie, for her love and wonderful companionship throughout the past 40 years of my life, from the very beginning of falling in love with her and also with the “Crossed Molecular Beams machine” (the question from Stephanie has always been, “Piero, who do you love more?”). Her lovely, ironic, humorous, brilliant, and unique personality and artistic creativity have always been the most precious and enjoyable gift to me. I love to have the walls of our home filled with her paintings, to attend her art shows, to see her creating, to have her with me in all that I do (except when “crossing beams”). I used to sing to her (with my out-oftune voice), “You are the sunshine of my life...”. Her ironic cartoons about “Dr. Casavecchia busily crossing beams” are still attached to the main chamber of my 30″ CMB machine and have been there for over 30 years!

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Autobiography of Piergiorgio Casavecchia: Forty Years of Happily

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