Special Issue Preface Cite This: J. Phys. Chem. A 2018, 122, 1159−1166
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Veronica Vaida: Autobiographical Notes Published as part of The Journal of Physical Chemistry virtual special issue “Veronica Vaida Festschrift”.
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INTRODUCTION I seldom think of the unlikely events that led to my move from Romania, where I was born, in Bucharest, on the third of August 1950, to Boulder, Colorado, from where I now write. Political turmoil in Romania in the early 1950s took our family to Cluj (Koloszvar, Klausenburg or Napoca) in Transylvania, the town that I still think of as home. My parents were from Transylvania: mother having grown up in Cluj and father born in a village nearby. They met however in Bucharest in the late 1940s having survived the war, father a political prisoner in a Romanian jail, mother a survivor of the Auschwitz concentration camp. They both spoke Romanian and Hungarian: father’s first language was Romanian and mother’s Hungarian. On arrival in Cluj, my younger sister Mariana and I were deposited in a Hungarian-only preschool where we acquired rudimentary language skills. I remember fondly growing up in Cluj, with the river Somes running through it, its old and lovely churches, parks, open markets, coffee houses and restaurants, theaters, opera housesa university town with a rich cultural life. When school started, I welcomed learning and most of all enjoyed the friendship and camaraderie of my schoolmates. My parents, like so many we knew, highly valued learning. Mother’s family counted a number of teachers and delighted in music and literature. Father’s family of poor and illiterate peasants, counted relatives, notably my grandmother and cousin Marioara, who in spite of significant hardship, were hard working, talented, and wise. Father regretted the limited opportunity to study and valued learning above all. My sister and I were told that the only inheritance we could have was the opportunity to learn. We were taught conversational French at home and practiced it during summer holidays. Once we acquired a basic vocabulary, French was fun and a gift later on as it opened up the possibility of reading beyond the limited offerings available in Romanian at that time. Summer holidays were free and happy, spent roaming the hills in remote Transylvanian mountain villages. Walks along the river banks and in the fields, hay rides with the neighbors and their children, drinking water from the well, playing with the chicken, pigs, and geese, smelling the wood fires at dusk, and the freshly baked breadall part of the memory of childhood. This fairy tale ended in 1963 when the Ceausescus came to power and our family had to move to Bucharest. This was a very difficult and unhappy event for me, having to abandon my friends, teachers and the familiar and much liked surroundings. Life was never the same again. Bucharest was a busy and intense place. My sister and I placed in a competitive high school. The school was rigorous and demanding while using the same material, textbooks, and requirements as all the Romanian schools. Discipline was highly enforced: we wore uniforms and had a strict dress code. School was free and supplies and uniforms highly subsidized. It was much later, by comparison with my daughter’s experience in © 2018 American Chemical Society
high-school in Boulder I appreciated how well my Romanian school had prepared me and my peers, many of whom were able to do extremely well anywhere in the world. After school, my friends and I read a great deal, found information on art, literature, philosophy, and other topics, which were not taught in school. Before long, however, we had to choose a career. Humanities were most appealing to me at the time but making a career in the humanities in Romania in the sixties was not a wise choice. After some heart to heart talks with father, I chose to study chemistry, not understanding until much later how interesting this would turn out to be. I am still discovering and rediscovering, with help from my students, colleagues, and collaborators, new and fascinating questions in chemistry. Admission to University was in a specific subject (chemistry in my case) and had a limited number of spaces since after graduation all were given a job. Entrance to university was based on sealed and secret exams in chemistry, physics, and math. My class of 200 at the University of Bucharest in 1968 had students from all backgrounds, from the whole country, about half women, half men. At University, we studied primarily math, physics, and chemistry with extensive laboratories. My peers and I worked hard, asked no questions, and built close friendships. I still count Marta and Rozalia among my best friends. All chemistry students were sent for a month in the summer for “volunteer” work in the vineyards in the Danube Delta under harsh and primitive conditions. We enjoyed every minute of it, my only regret being that I only did it for one summer. One day in the spring of 1969, a notice was posted on the university gate that a fellowship would be available for study in the USA for someone who was in chemistry, in their first year, had good grades and could compete in exams in chemistry, physics, and English language. We had heard of such fellowships but none existed yet in chemistry. My professors suggested I should try, mostly to see if I had learned anything in that first year at university. Two of us received the grades required and having heard nothing more, continued work and play until, unexpectedly, in late December 1969, were told to pack our bags and journey to universities assigned to us. All the information I received at the time was that I would be on my way to Brown University, Providence, RI.
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BROWN UNIVERSITY: CHEMISTRY AND SO MUCH MORE Brown University provided an unexpectedly friendly, charming, and welcoming environment for the transition to the US, a very different cultural and academic setting from the one I knew in Romania. From the moment I arrived in Providence, just after Christmas 1969, my host mother, Mary-Louise Record took me home and took charge. She introduced me to the first supermarket, where I immediately got lost in the aisles devoted Published: February 8, 2018 1159
DOI: 10.1021/acs.jpca.7b12802 J. Phys. Chem. A 2018, 122, 1159−1166
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The Journal of Physical Chemistry A to salad dressings! She opened my first bank account after discovering that I carried small bills in my pockets to pay for tuition, room, and board (ours was a cash economy). Mrs. Record was the head of Brown’s foundation and always on campus, ready to answer questions, such as how to navigate the university or who Dracula was! She took me to all the hockey games where I learned about the Ivy League and was introduced to many important people. A few years later, at the end of my Ph.D. at Yale, while interviewing at Harvard for an independent postdoctoral position, I encountered Don Hornig, who had been president of Brown University during my time there. In 1977, after my interview talk, he was telling the Harvard chemistry faculty stories about all the silly things Veronica did when she first came to the US, told to him by Mrs. Record. The stories must have been most entertaining since I did get the position. My English language skills were limited and I was learning rapidly the meaning of words from their context. This approach worked reasonably well at Brown. However, on my first visit back from Yale where in 1973 I had started graduate school, I was summoned by Mary-Louise halfway through dinner, into the kitchen to be told I needed to clean up my language. The problem was that I did not know which part needed cleaning. At Yale I met a wonderful group of older graduate students who remained my life long friends with Barney Ellison in the lead. My English developed under Barney’s tutelage but in ways I did not understand. I had to take a step back and be very quiet for a while. As it was, language was not my main challenge at Brown. Socially, I was unable to read the everyday clues of accepted and unaccepted behavior. Academically, while having more training in chemistry and good study skills, I was unaccustomed to making choices and asking questions, which made finding my place in the program a challenge. Brown was wonderful in every way, providing a supportive environment to work, a helpful and friendly foreign student and scholar’s office and an extremely impressive academic staff. As I failed to choose the right courses for my first, spring 1970 semester, I was assigned a mixture of sophomore organic and junior physical chemistry courses with the expectation I would find the right level. I failed all the first hour exams but in the process learned to appreciate the differences in the educational system at Brown and the one I came from and did very well by the time of finals. The Pembroke Campus was perfect! I remember fondly the little cafe that, close to midnight, served the best peppermint stick ice cream sundaes for 25 cents. In time, I met some of the students in my classes (Helen Hollingsworth, Sue Brewster, Cynthia Watson, Erik Einstein) and realized what a special group of young people these were. I do not think I met anywhere accomplished young women such as those I knew in the Pembroke dorms. They were academically accomplished, intellectually interesting, socially involved, and great company. I remember the spring of 1970, studying for finals with “Let It Be” coming from every open dorm window. I regret that I was not able to stay longer at Brown and choose interesting courses to take but the fear that I would not be allowed to return to finish my degree motivated my graduation in 2.5 years. The best part of my program at Brown was research, which I did in the group of Prof. Ned Greene. Professor Greene and his group made research fun and meaningful and provided a home. In the lab, I was trying to build a new detector for molecular beam experiments. I greatly appreciated the elegance of experiments in Prof. Greene’s lab, which in spite of their
simplicity, provided insight about molecules and their reactions. Ned Greene would come in on Saturday mornings to teach me to blow glass and to wind electromagnets. He and all my Brown professors were impressive, insightful, and caring. They gave me individual attention as well as my parents and my sister during their visits. I learned much more than chemistry from them all. Soon enough time came to think of the next step. While I enjoyed all my courses at Brown, my research experience in Ned Greene’s lab and my interests pointed to graduate work in physical chemistry. Prof. Greene seemed impressed with my research and advised applying to only a few graduate programs. The most memorable interview was at MIT where faculty met with prospective students. Jim Kinsey came to visit Brown soon after my admission was denied and kindly explained that he made the decision thinking that I was far from aggressive enough for MIT, no doubt true. Of the three programs I did apply to I was admitted to Yale where I started graduate school in the fall of 1973. The summer of ’73 was special in many ways. The trip home involved a stopover in Prague where I was taking a small bag of electronic components to Zdeněk Herman. Zdeněk gave me an unforgettable day long tour of Prague and talked about life and science at Yale as well as a place he loved but I had not yet heard about: Boulder, Colorado. It was a privilege to interact through the years since with Zdeněk on many occasions in Prague and in Boulder.
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GRADUATE WORK AT YALE I arrived at Yale anticipating explorations of physical chemistry, the university, and its traditions. The summer of 1973, on break in Bucharest, my sister provided the opportunity to research and write history of architecture papers, which I focused on the Yale campus. Once there, it was very exciting to walk past Eero Saarinen’s buildings, Philip Johnson’s Kline tower, and the Beinecke Rare Book and Manuscript Library (SOM) in addition to the Gothic buildings of the Memorial Quadrangle. On such walks, we often stopped at the Grove street cemetery to pay homage to Josiah Willard Gibbs Jr. Each walk, then and now, was an opportunity to discover and rediscover the treasures of Yale University. By contrast, New Haven lacked charm and made up for it in danger. I seldom wandered into New Haven except toward the end of my stay there, when I met and befriended fellow Romanians Nicolae and Maya Simionescu who returned in the mid-70s to create in Bucharest a successful Institute of Cellular Biology and Pathology at a time when little research of any kind was possible in Romania. Finding a research home and mentorship was at first difficult. Physical chemistry had once been a very strong program at Yale but not so in 1973. Few faculty remained in physical chemistry, and to my surprise, some responded to my interest in pursuing research in experimental physical chemistry by pointing out that this kind of work was unsuitable for women. There were no women on the Yale chemistry faculty, and some of the senior professors unable to conceive of a women colleague, clearly stated their opinion, to the dismay of the graduate students. My early academic work in Romania had not prepared me for this attitude: admission to the University was based on secret exams and as a result more then half of the faculty and student body in chemistry were women. An important break in my career at Yale came in the fall, in the library, when Kevin Peters approached me and introduced me to a close knit group of dedicated graduate students in physical and physical organic chemistry (Barney Ellison, Paul Engelking, Matt Platz) with Barney acting as the de facto mentor. Later on, postdoctoral 1160
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not have the words to express the significance and impact that April 1, 1977, had on my future.
fellows, including Branka Ladanyi, Glenn Evans, and Bill Watson, arrived. Glenn Evans is my oldest friend and colleague in the US since we met in the early 70s at Brown. Daily lunch in the Kline Tower, often joined by Marshall Fixman, became a tradition, as was dinner where we shared cooking and eating together before returning each evening to the lab. My fellow students and postdocs from Yale became collaborators, mentors, and friends. After a few false starts, with advice from my friends, I joined the research group of Steve Colson to work on molecular spectroscopy, which I understood could be used in many ways to investigate molecules in different environments. During the day, with Steve as my adviser, I learned to make crystals of benzene with control over their composition and look at their spectra at 2 K to study energy transfer mechanisms. At night and on weekends, following up on interesting new developments in the literature and lengthy discussions with my friends, I tried experiments using optoacoustic spectroscopy, thermal lensing, and multiphoton ionization. It was all great fun and the few experiments that worked I shared with Steve Colson who incorporated them into his program. There were no lasers at Yale in the mid-70s, with the exception of Geraldine Kenney Wallace’s research in pulse radiolysis which we, the graduate students, got involved with since Geraldine, an instructor at Yale, was an inspiration as a researcher and teacher. Her position of Instructor did not allow her to mentor Ph.D. students. She was discouraged at Yale from interviewing for a faculty position and left in 1974 to set up the first ultrafast spectroscopy lab at the University of Toronto, in Canada. Meanwhile, Paul Engelking having decided to obtain the spectrum of a molecular ion was building with no resources a nitrogen laser of his own design using aluminum foil, paper clips, and a discarded capacitor. There was nothing Paul could not do so we were not surprised when he built his laser and obtained the spectrum of N2+. The group of graduate students, postdoctoral fellows, and undergraduates like Steve George, now my colleague in Colorado, made the Yale experience an amazing journey into research. Memorable in our scientific development were meetings between our group with the spectroscopy groups of Elliot Bernstein at Princeton, Dave Hanson at Stony Brook, and Bryan Kohler at Harvard: the PIs having been contemporaries of Steve Colson’s at CalTech in G. Wilse Robinson’s research group. These meetings provided insight, context and a community for molecular spectroscopy. In the spring of 1977, at the end of my Ph.D., I was thinking of pursuing a postdoctoral position in the US. Science in Romania along with all other intellectual pursuits was suppressed, and the fate of those tainted by exposure in the “West” uncertain. My search for a postdoctoral position halted when I could not get a letter of recommendation from my adviser. A chance encounter between Bill Reinhart (whom I did not meet until much later but who talked to my friends Barney Ellison and Paul Engelking, postdocs at JILA) and Dudley Herschbach, then Chair of the Department of Chemistry at Harvard, provided the opportunity for me to interview and receive a position as an independent postdoctoral fellow, a position funded by Xerox. My interview at Harvard was everything I could have hoped for as I gave the first presentation on my research, discussed with Dudley Herschbach the big picture problems in physical chemistry and with Bill Doering energy flow in molecules. Dudley assured me that the Harvard faculty will make up its own mind about my work and would not need a letter of recommendation. I do
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HARVARD: SPECTROSCOPY AND REACTION DYNAMICS In 1977 and 1978 I took many trips to Princeton where Kevin Peters was a postdoctoral fellow with Meredithe Applebury, working at Bell Laboratories on the time-resolved cis−trans isomerization of rhodopsin. Meredithe remains a close friend and consultant on issues involving life, science, biochemistry, and biophysics. The only unsuccessful joint project was Kevin and Meredithe’s attempt to teach me to ride a bicycle! In the spring of 1978, Kevin received a faculty position in chemistry at Harvard and we decided to get married. On the morning of our wedding day, Dudley Herschbach asked me to his office and presented me with the offer of a faculty position in chemistry. While Harvard has had a number of talented and influential women chemists, I was the first to be granted a faculty position: as Mary Fieser pointed out, I was fortunate to be born late enough for this to be possible. My colleagues at Harvard were extremely supportive and many remained close friends. I was extremely pleased and humbled, years later to receive the American Chemical Society E. Bright Wilson Award in Spectroscopy since Bright and Thérèse Wilson have been friends, mentors, and supporters during my time at Harvard and since. George Kistiakovsky had a lot of fascinating stories to tell of science and wars. Personal and scientific interactions with Martin Karplus were and continue to be important. Dudley Herschbach and Bill Klemperer and their groups made my work possible. My contemporaries, Kevin Peters, Chris Dobson, and John Cooper, provided a friendly and inspirational peer group. I learned from them about the value of ideas over money, of original thought over quantity of publications or grant size. While several senior colleagues expressed concern about my working after having children, they celebrated with us the birth of Katherine in 1981 and Paul in 1982. Support from my colleagues, my students who came home to work with me on the papers reporting our first results, excellent day care, and the arrival of my sister, Mariana, and her invaluable help made it possible for me to continue working. Mariana, an accomplished architect, was always available to look over and look after my children even when I could not. A couple of years earlier, as I approached the end of my graduate work at Yale, I had understood the power and insight possible through spectroscopy. However, it also became obvious that molecules that had interesting dynamics underwent large changes in geometry on excitation, and reacted producing messy and diffuse spectra of limited use. I took the challenge to understand reactive molecules to Harvard. The independent postdoctoral position was, in retrospect, an effective way to develop my own projects. Since no funds or laboratories were available, the challenge was substantial but the research environment and colleagues inspirational. Frank Westheimer on occasion held lunches and in 1978 he invited me to join an illustrious group of senior physical and physical organic chemists. On my way out Frank asked me to tell them what I intended to do. I was unprepared and made rather a mess of this presentation, but when Frank understood I was interested in photoreaction dynamics he asked me if I had considered looking at photoaffinity labeling reagents. After lunch I returned to my desk and wrote my first research grant, which was awarded by NIH. Later I received grants from NSF, which provided support through most of my career. 1161
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The Journal of Physical Chemistry A The first year of my independent postdoc I was thinking about and talking about reactive molecules with the students and postdocs in the Herschbach, Klemperer, and Wilson groups. They were the reason I started to develop spectroscopy in supersonic jets: without their insight, technical prowess, and experimental help I could not have done any of what followed. I decided to use absorption spectroscopy of jet-cooled molecules to eliminate inhomogeneous effects so as to better understand molecular excited electronic state structure and dynamics. At the time, absorption was deemed unsuitable for studying jetcooled molecules and more sensitive methods based on fluorescence or multiphoton ionization were used. These techniques, however, relied on long excited state lifetimes and were not useful for reactive systems. Molecules in which efficient and chemically interesting reactive channels shorten the excited state lifetime give rise to diffuse and uninformative absorption spectra, and little to no fluorescence. I had hoped that cooling molecules in a supersonic jet eliminated inhomogeneous effects, simplifying spectral analysis. I had settled on using lamps rather then lasers for this experiment. While very low tech, in an era were lasers were all the rage, lamps allowed for high duty cycles, more accurate relative intensities, and an energy range from the IR to the vacuum UV. The S/N calculations were suggesting that the increased absorption cross sections of interesting molecules in the UV would enable the absorption experiment. One evening, a skeptical Garry McClelland did his own estimates: it was most encouraging to come in the next morning to find his note and numbers showing that the experiment would work. Garry, Chuck Joyner, Kit Bowen, Jim Lisy, Jim Valentini, Ken Leopold, Ed Quitevis, and the other Herschbach and Klemperer colleagues opened up the vast surplus equipment storage and helped me assemble the first instrument. This experiment was extremely low tech, built of a glass sewer pipe, but most importantly worked! Not long after its initial success the instrument exploded on shut down, just before a HarvardMIT evening seminar, allowing for a large audience to inspect the disaster. I had caused this incident by codepositing on the cold trap a lecture bottle of butadiene along with another bottle of NO2. Bits of glass were found for years afterward in the basement Klemperer lab, where I set up the first version of this experiment. Over the next few years, with many modifications, the jetcooled absorption spectrometer provided a wealth of data for reactive molecular excited states. Jamie Donaldson with Erik Richard in Colorado using a high resolution Fourier-transform Bomem spectrometer developed the best and last version of the instrument. Among the first successful studies in my group using jet-cooled absorption were those of the 1Bu+ ← 1Ag− transition in small polyenes. The spectra obtained by Doreen Leopold and interpreted by Rus Hemley, with a great deal of insight from Martin Karplus and his group, showed dramatically different photophysics for butadiene, hexatriene, and octatetraene, providing new information on electronic structure and photodynamics in this system. At the time (1980s) spectroscopy was used primarily to obtain electronic structure. Our group was able to investigate instead small dissociative molecules such as CS2, OCS, H2S, and NH3, which undergo large changes in geometry on excitation. For example, the pyramidal ground state of NH3 becomes planar on excitation and dissociates to NH2 and H. The jet-cooled spectra in Maureen McCarthy’s Colorado Ph.D. thesis were modeled theoretically in collaboration with the excellent team of
Rosmus, Werner, and Botschwina to show that mode coupling was necessary to explain the spectra and the photoreaction dynamics. To broaden the scope of our work we started a program to investigate forbidden states of highly symmetric molecules, specifically choosing transition metal carbonyl compounds. The experiment involved two-photon excitation followed by ionization and required a laser. Commercial lasers were scarce and at any rate; no funding was available. In response, I teamed up with Chuck Joyner in the Klemperer group to build an excimer laser. The process was fun and a laser was built. Working with Chuck was a real privilege. Soon, the laser enabled the study of transition metal complexes by my young group. The awesome team of Lewis Rothberg and Dan Gerrity performed the first experiments. Instead of observing the symmetry forbidden states, we expected on two-photon excitation of Cr(CO)6, they found sharp lines which on inspection turned out to be transitions of atomic Cr. Excitation of this complex in the gas phase removed all ligands! The question we followed up on was the competition between metal−metal and metal ligand bond cleavage. Collaboration with Richard Bernstein (then at Columbia), Kevin Peters, and John Cooper at Harvard allowed my group (Jean Welch, Doreen Leopold, Dan Gerrity, and Lewis Rothberg) to prepare metal−metal and metal−sulfur clusters in the gas phase, which, in Colorado, Doug Prinslow investigated systematically. The spectroscopy and reactivity of clusters became a main theme of my group. Ron Naaman came to Harvard to work with Dudley Herschbach and we had an opportunity and a lot of fun developing ideas about cluster experiments. Seven years later, when Ron Naaman came on sabbatical to JILA and Jamie Donaldson and Steve Sapers were doing experiments using CH3I clusters, Ron, an inspiration for my group, along with Mark Child, who was also on sabbatical, helped obtain and understand the spectral shifts we were observing in CH3I clusters. The spectroscopy of acetone and aldehyde clusters benefitted from the experimental work of Geoff Gains, a talented undergraduate, and the expertise in molecular spectroscopy of my colleague Stew Strickler. The cluster research turned out to be most interesting, later on, in an atmospheric context focusing on hydrogen bonded water clusters.
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COLORADOLIFE AND WORK A change was forthcoming given the tenure rate at Harvard in the early 1980s. As we considered options, the University of Colorado stood out as a very interesting possibility for both Kevin (a physical organic chemist) and me, but there was little precedent for related people being hired in the same department anywhere at that time. The interview process lasted about two years, with multiple visits. I remember one of my week-long interview trips, while 8 months pregnant, with meetings back to back on the top stories of different buildings. My sandals broke during one of the seminars. I remain grateful to Veronica Bierbaum for her help recovering from being on stage, barefoot and pregnant. Barney Ellison and Sally Sullivan provided a welcoming home during these trips. After the lengthy interview process, the University of Colorado offered me a position and the opportunity to prove myself. Kevin and I with 3 year old Katherine and 1.5 year old Paul moved to Colorado. The very best of Boulder was finding Bixby school where my children remained for 10 years learning how they could think through most problems and how much fun it was. 1162
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great friendship. I worked with Susan to write the paper on the potential consequences of the OClO photoreaction dynamics to the polar ozone: as a result, many of my graduate students followed careers in atmospheric science. OClO was full of surprises: its chemistry in water and on ice produces Cl + O2, different from the gas phase where the main reaction channel is formation of ClO + O. We pursued the condensed phase reaction in aqueous solution with John Simon at UCSD where Erik Richard’s first attempt at working in water led to a mild if spectacular explosion. The chemistry of OClO on ice was a collaborative project led by Laura Brown in my group with Jeff Roberts at the University of Minnesota and Dave Hanson at NOAA. This molecule opened the way for extremely interesting environment specific reaction dynamics with potential consequences in the atmosphere. The importance of the reaction environment was well-known to us but considering the atmosphere, it became obvious that water and aqueous multiphase environments had to be investigated. Cluster studies continued but now we worked exclusively on water clusters, and in doing so, given the tendency of water to condense and readily form hydrogen bonds, we turned away from supersonic jets to use equilibrium cells, an even lower tech experiment than we had employed before. I had started to think about chemistry in clusters possibly relevant in the atmosphere, and early on, John Birks helped define the issues associated with ozone−water clusters. Greg Frost in collaboration with Ron Naaman and Yinon Rudich, a graduate student in Ron’s group at the Weizmann, explored the possibility of forming OH upon irradiation of ozone−water clusters. At the time, a discrepancy between measured and modeled atmospheric absorption termed “anomalous cloud absorption” was being highlighted in the literature. The unknown absorption was in part in the near-IR and responded nonlinearly to the water vapor partial pressure: based on my group’s work with clusters, the possibility that water clusters and their vibrational overtone transitions could be part of this effect suggested itself. I naively assumed that all the information neededvibrational overtone spectra of water clusters and information allowing abundance estimateswas available in the physical chemistry community. Lisa Goss in my group worked at modeling this problem, only to find that both abundance calculations and vibrational overtone spectra were challenging to obtain under atmospheric conditions. To calculate equilibrium constants, the free energy change must be obtained: for a relatively weakly bound cluster at the 200− 300 K temperatures typical in the atmosphere, the statistical mechanics was not available. Thus, the atmospheric problem suggested fundamental theoretical studies to the physical chemistry community. The spectroscopy in the mid-IR of water clusters posed another challenge due to the large line widths, which to this day make observation of the cluster overtone transitions a challenge. Just as we were pondering how to best estimate the near-IR absorption of water clusters, at a conference in Australia, I discovered that Henrik Kjaergaard having just started a faculty position at Dunedin in New Zealand, was to present a poster on calculated vibrational overtone spectra of water clusters! He soon came to Boulder on a sabbatical when we did work out some of the theoretical estimates for water cluster spectra needed for modeling their effect, atmospheric modeling done with John Daniel at NOAA. Henrik Kjaergaard, now at the University of Copenhagen, and our groups have worked together on this and other problems and our collaboration continues. Important to this story and
Bixby turned out to be especially important to us as in 1990 Kevin and I divorced. Pat Baker and Bart (Harlan Bartrum), founders of Bixby school, became close friends and helped raise Kay and Paul to be the most wonderful children I could have imagined. The move to Colorado was in many ways difficult but thanks to Maureen McCarthy and Doug Prinslow, my first Colorado graduate students, a lab was set up in the subbasement of Ekeley with bits and pieces discarded in the renovation of the biolabs. This do it yourself setup allowed us to work most of the time for 25 years until an impossible-to-eradicate cockroach infestation accelerated the move of my group to the main floor of Ekeley where our lab still is today. Thinking back to the challenges of the subbasement lab, one event comes to mind. One Friday evening, while Maureen was in the lab, sewage started seeping through the walls and then pouring in from a door near the ceiling. At the time, the atrium between the CIRES Ekeley building and the chemistry building was under construction and the work crew had punctured a sewage line. They decided to get back to it on Monday not realizing that our laboratories would be in the way. Maureen dealt with the emergency efficiently and promptly and we were able to get back to work relatively soon. Other challenges were the lack of access to a modern instrument shop, a problem for experimental physical and physical organic chemists in the department. Barney Ellison through heroic efforts, in due time, was able to set up a state of the art instrument shop that has and continues to make our work possible. The experiments we set up were building on our work on the spectroscopy and photoreaction dynamics of small molecules and molecular clusters. At JILA I encountered Jamie Donaldson who then joined my group as a postdoctoral fellow, at the same time with graduate students, Maureen McCarthy, Doug Prinslow, Anne Jefferson, Steve Sapers, and a little later Erik Richard, Kathy Lantz, Laura Brown, and Geoff Gains, a talented undergraduate. They and visitors such as Ron Naaman, Mark Child, Pavel Rosmus, and Eckart Rühl made significant contributions to our work on small molecule dynamics. The jet cooled absorption spectrometer was working well, Erik Richard, an amazing experimental scientist, had joined the group and I elected to study the excited state of OClO. Erik learned from the jet cooled absorption spectra that not only the asymmetric stretch leading to ClO + O was active but also the bend and symmetric stretch had short lifetimes, suggesting that Cl + O2 was also possible. The rich chemistry of OClO was foretelling of a change in emphasis in my research.
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PHYSICAL CHEMISTRY INTERFACES WITH ATMOSPHERIC AND ENVIRONMENTAL SCIENCE In Boulder, the first rate research programs focusing on the environment were inescapable and, while I did not anticipate it before coming to Colorado, caused a welcome change in my thinking about science. In 2000, I was elected as fellow of the Cooperative Institute for Environmental Research (CIRES), which helped connect my group to NOAA and to environmental research. The paradigm change came early on, in 1988 when Susan Solomon, having heard from Eldon Ferguson of our OClO work, came over to ask if I understood the implications of this work to polar ozone. I did not, but when Susan explained the chemistry to me, I realized that many of the issues we were studying using model compounds could provide insight and mechanisms for atmospheric chemistry. That day was the start of a very interesting collaboration and a 1163
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estimated cross sections, we worked with Michael Mills and Brian Toon to provide the new inputs to models. This mechanism explained many of the discrepancies between models and measurements in the SO2 vertical profiles on Earth and has been considered, with limited success, in models of the middle atmosphere of Venus. Understanding the chemistry of SO2 in planetary atmospheres continues in my group with the work of Jay Kroll who has been investigating reactions of excited electronic states of SO2 with water and with alkanes to lead to aerosol formation. The Kjaergaard group is, once more, providing the theoretical support. Karl Feierabend, and Nabilah Rontu in my group, evaluated other potential vibrations that could be excited to drive chemistry. We learned that the OH stretch has significant advantages over all others due to the large vibrational frequency, and the anharmonicity of the potential. Interestingly, in Earth’s oxidizing atmosphere, OH stretches abound. While we were very pleased with these results, my group soon realized that this concerted chemistry could be extended to organic acids and alcohols. Specifically, we investigated the vibrational overtone pumping of pyruvic and glyoxylic acids and of gem diols formed on hydration of aldehydes. Important contributions to this work came from Meghan Dunn and George Shields. The experimental team consisted of Katy Plath, Jess Axson, and Molly Larsen in my group working with Kaito Takahashi, Zeb Kramer, and Rex Skodje on the theory. The results suggested that direct dynamics occurs on subpicosecond time scales and drives a concerted decarboxylation reaction by hydrogen atom chattering. The credit for this elegant mechanism belongs to Rex Skodje. These concerted vibrational overtone driven reactions have been fundamentally new in physical chemistry and can contribute to atmospheric photochemistry in predictable ways.
several to come, was my meeting Adrian Tuck in 1993: we were married in 1997. Adrian, then at the NOAA Aeronomy Lab, had an unusual background having been trained in physical chemistry and then in meteorology: he was able and helpful in making the connection between water clusters and atmospheric absorption pointing out that the square dependence observed on water vapor pressure has been an unresolved controversy since 1973! Absorption by water clusters can make a contribution to radiative transfer, and interestingly, with increased temperatures, clusters can provide a nonlinear enhancement in the anthropogenic climate change. Hydrogen bonded water clusters with trace gases turned out to be interesting for atmospheric chemistry: Lisa Goss, Jill Headrick, and Marta Maron obtained spectroscopic information for a number of interesting examples. Throughout my work radiation was crucial as a spectroscopic probe and as a driver of excited state reactions. My group had looked primarily at electronically excited states, and in targeting atmospheric problems, used mostly solar simulators (filtered Xe lamps). This work continues with recent studies by Rebecca Rapf, Allison Reed Harris, and Jay Kroll on building complexity in planetary environments by sunlight. In 1997, I was talking with Greg Frost, now at NOAA, about OH radical formation at dusk and dawn observed by Paul Wennberg in Jim Anderson’s group without a plausible mechanism to explain the observations. Jamie Donaldson, who was visiting from Toronto, and I remembered the beautiful work in physical chemistry of overtone pumping of molecules like H2O2 and HNO3. Adrian added HNO4 as the potential culprit in the lower stratosphere. These molecules have weak bonds and therefore can dissociate with red light following excitation of the OH stretch. Jamie, Adrian, and I celebrated the idea, and soon after, with help from Greg Frost and Karen Rosenlof modeled this effect, which could be a factor at very high solar zenith angles where electronic states could not be excited. Adrian presented this possibility to the atmospheric community who likely would not have known of this result otherwise. Both the atmospheric and physical chemistry communities were skeptical and for a good reason: the cross sections for exciting OH vibrational overtone transitions in these molecules are extremely low, and while the effect is real, it is limited to light from the Sun near the horizon where only visible radiation is available and electronic states cannot be excited. The new aspect of this work was the demonstration that overtone pumping studied by physical chemists can explain the observed OH radical formation at dusk and dawn in the atmosphere. My collaborators and I continued to think of vibrational overtone pumping in molecular systems where electronic state reactions would not occur. Another visit by Jamie Donaldson, a walk to campus, and the possibility emerged that the molecule to study was H2SO4. Electronic states of sulfuric acid are very high in energy. Also, all bonds in the molecule are strong so that the mechanism studied by physical chemists using overtone pumping would not be possible. Here, a concerted reaction leading to SO3 and H2O occurs by a mechanism suggested later by Yifat Miller and Benny Gerber. Paul Hintse carried out the initial experimental work in my group. Later on, Dan Havey and Karl Feierabend with advice from Steve Brown (NOAA) built a cavity ring down spectrometer with much higher sensitivity in the near-IR and visible that allowed spectroscopic studies of OH vibrational overtones. Fortunately, Henrik Kjaergaard was on sabbatical in Boulder at the time and took charge of the theory. Once we had a mechanism and
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CHEMICAL COMPLEXITY IN PLANETARY ATMOSPHERES INCLUDING THE CONTEMPORARY AND ANCIENT EARTH Another interesting change in my research came serendipitously one Friday night, over dinner after a physical chemistry seminar. In response to Barney Ellison’s graphic comments about organic radicals, Adrian suggested we should look at the interesting results obtained by Dan Murphy at NOAA, and that physical organic chemistry ideas would be important to consider. Following up on Adrian’s cryptic suggestion, we learned that observations of organic fragments on single aerosol particles in the atmosphere puzzled the aerosol community since organics, mostly insoluble, were not supposed to be on aqueous aerosols. And yet field measurements found organics even in the lower stratosphere. With Adrian’s advice and coaching, Barney Ellison and I pondered these findings on our frequent visits to Starbucks. The picture that emerged suggested that the likely insoluble organic molecules would form a surfactant layer on the aqueous saline solution, which constitutes the aerosol. The organic layer would limit the growth of the aerosol. Soluble species would be dissolved in the aqueous core while organic molecules could dissolve and be transported in the organic layer. In the atmosphere, oxidation would functionalize the organic species and radical reactions would change the hygroscopicity of the aerosol. The study of aerosols changed in response to these ideas to emphasize the organic layer, which would affect the optical, morphological, and chemical properties of aerosol particles. Barney Ellison was excited and “selling” this idea to all he knew: it was imperative that we write a paper describing this model as soon as possible. 1164
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The interest in organic films at aerosol water−air interfaces and their properties in the contemporary and ancient Earth’s atmosphere, led to a retooling of my lab. We purchased Langmuir troughs and proceeded to explore the thermodynamic properties of organic films at the surface of water. While the experimental approaches were new to my group, they did draw on the spectroscopy as a function of the reaction environment I have been working with since graduate school. The work was started by Theresa Williamson and developed by Jessica Gilman who was able to explore the permeability, stability and chemistry of organic films at the water−air interface. Oxidative chemistry of organic films involved collaboration between my group and visitors including Heikki Tervahattu, Dan Cziczo, then at NOAA, Jamie Donaldson, University of Toronto and Baagi Mmereki from his group. With these approaches, Nabilah Rontu investigated a very interesting system of perfluorocarboxylic acids, which are not very soluble in either aqueous or organic phases. Her work, of interest to Dupont, showed that these compounds could be transported on atmospheric aerosols. Using Langmuir troughs, Elizabeth Griffith and Russell Perkins, with help from Heather Allen at The Ohio State University, have investigated the interaction of small molecules with phospholipid films, combining the experimental information from our lab with molecular dynamics performed in collaboration with Martina Roeselová and her collaborators in Prague. The troughs have provided control over samples studied with surface reflection spectroscopy, which my group developed. Using surface reflection IR spectroscopy (IRRAS), Elizabeth Griffith explored differences in the state of ionization of phenylalanine between the water surface and the bulk aqueous phase. These studies culminated with Elizabeth using IRRAS to show that, at the surface of water, peptide bonds could be generated nonenzymatically, a stumbling block in prebiotic chemistry. Russell Perkins took the research on surface lipid films one step further using membrane enclosed vesicles to study the effect of phenylalanine on the vesicle stability, in an attempt to understand the molecular level mechanisms operative in phenylketonuria. The few examples our group studied of processes confined at the surface of water, on drops, or on vesicles demonstrate that confinement at water interfaces provide fundamentally unique reaction environments, relevant to the contemporary and prebiotic Earth. The versatility of chemistry in different phases and at interfaces of water became obvious through our studies embedded in the recent literature. My group’s effort on sunlight driven organic multiphase chemistry started with Elizabeth Griffith’s attempt to look at the photochemistry of pyruvic acid in aqueous solution. However, as soon as she started the solar simulator, the lab filled up with an overwhelming scent. The photochemistry of this molecule in the gas phase was an old friend to us but nothing we knew prepared us for this outcome. We could not isolate and identify the compound responsible and gave up on the project. Barry Carpenter was just then visiting the department and took a detour to our lab to sniff it: he immediately identified the culprit as acetoin and wrote down the aqueous phase photochemical mechanism for pyruvic acid. Shortly, with help from Rich Shoemaker and NMR we confirmed Barry’s predictions. Without Barry and his chemical insight none of the organic photochemistry studied by my group since 2013 would have been possible: we learned a great deal of organic chemistry from Barry and hope to continue to do so. Simultaneously, several collaborations informed on the
With a very steep learning curve since I did not have any background in aerosol science, a draft was written with contributions from all of us. The paper was extremely difficult to publish since proof of the surfactant layer was not available at the time. However, with an alphabetic author list, Ellison, Tuck, and Vaida “Atmospheric Processing of Organic Aerosols” was published in 1999. A couple of years later, Heikki Tervahattu contacted me about interesting observations of aerosols collected in Finland. Heikki visited and shared TOF-SIMS data of collected marine and then continental aerosols, which clearly had an organic layer, composed primarily of fatty acids. Heikki’s sabbatical provided the missing proof and was in scientific and personal ways a very rewarding experience. At the end of 1999, just as our aerosol model was developed, another serendipitous event changed the direction of my work once more. Chris Dobson, an old friend and colleague from Harvard (then at Oxford, now at Cambridge in the UK) was visiting briefly, at the end of a conference he had attended. While I was scrambling eggs for our breakfast, Chris asked about our aerosol model. I described the aerosols as saline solutions surrounded by an organic film, which become airborne and travel exposed to different temperature, humidity, radical, and radiation fields. Chris asked about the size of these aerosols, which I knew to be a few microns in diameter upon which Chris saw the similarity between them and single cell bacteria. After this eureka moment, on the way to the airport, we further speculated on the analogies of aerosol processing with metabolism. In searching for a primitive form of replication, I mentioned offhand that aerosol coagulation and division could provide such a mechanism. As soon as I mentioned this idea to atmospheric scientists, my ignorance was obvious and I was sent to all the important textbooks in the field, which treated aerosol coagulation but not division. The point was that a spherical shape minimized surface tension, and so division was not thermodynamically possible, at least not in a homogeneous droplet such as one composed of sulfuric acid and water. I was able to show to Adrian’s satisfaction that coagulation of aerosols with organic coatings would exceed the surface area available and could drive division. We eventually convinced Jamie Donaldson to help with the thermodynamic arguments leading to a couple of papers, largely unread. Interestingly, the fission enabled by the surfactant film was asymmetric, with one daughter being the size of bacteria the other the size of viruses. Following Chris Dobson’s visit, I met up with Adrian at a meeting at the Hague and shared Chris’ analogy of aerosols and single cell bacteria. Given our complete lack of background in prebiotic chemistry, we went to a bookstore, purchased anything we could find on origin of life research. Adrian could read a book a day and remember everything he read. I was much slower but soon realized that the main advantage was that the surface of aerosols would concentrate and align organics providing a very special reaction and self-assembly environment. It was great fun developing the ideas that Adrian put down in a manuscript “Atmospheric aerosols as prebiotic chemical reactors”. I gave my colleague and friend Tom Cech an early draft: his comments were extremely helpful in understanding the background in the field and the assumptions of the “RNA World”. This paper was extremely difficult to publish but eventually Susan Solomon communicated the paper by Dobson, Ellison, Tuck, and Vaida (in alphabetical order) to Proceedings of the National Academy of Sciences with the date of August third, 2000, my exact 50th birthday. 1165
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toward a molecular understanding of complex chemical problems.
problem. Anne Monod, a CIRES visiting fellow on sabbatical, inspired the suggestion that the carbon−carbon bonds produced on excitation of an oxoacid, in and on water could be a source of prebiotic lipids. Becky Rapf investigated the detailed aqueous phase chemistry of oxoacids as a function of composition, pH, etc. Elizabeth and Becky were supported by NASA astrobiology fellowships for prebiotic chemistry. Having acquired the background in the origin of life, they performed their studies under conditions relevant to the oxidizing atmosphere today as well as prebiotically, where no oxygen was present. Becky Rapf was able to show that organic photochemistry of oxoacids generates new lipids and drives oligomer formation in mixtures of fatty acids and alcohols not themselves amenable to photochemistry in the lower Earth atmosphere. This work, with help from Anne Monod and Barbara Ervens started a major effort by Allison Reed Harris on the multiphase chemistry of pyruvic acid. An extraordinary opportunity presented itself through collaboration with JeanFrancois Doussin to look at fundamental chemistry under conditions relevant to the atmosphere in the French simulation chamber CESAM. As the results from CESAM and from our Boulder lab appear, we continue to marvel at the different possibilities and chemical pathways that open up for this small molecule under atmospheric conditions. The interesting and powerful instrument (CESAM) and the even more impressive team headed by Jean-Francois are compelling. For me this collaboration provided a home away from home, valued professionally and personally.
Veronica Vaida
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ACKNOWLEDGMENTS TOWARD THE END And now, toward the end, as I recounted my meanderings through science, I must remind my readers that all this work was supported by large scientific communities. They helped phrase the questions, generated controversy, and sometimes led to answers: it has been and remains a privilege to belong to this international community of scientists. In retrospect, my fundamental work on spectroscopy and reaction dynamics allowed for contributions to understanding radiation, aerosols, chemistry, and climate in planetary environments including the contemporary and ancient Earth. Pondering the relevant questions in atmospheric science has often lead to hitherto unexplored fundamental physical chemistry. Physical chemistry, the quantitative expression of the behavior of molecules, is essential for both diagnosis and prognosis. The intellectual content at the interface of physical chemistry and atmospheric science is fundamental to finding solutions to real problems still unresolved. My daily interactions with my colleagues in the department as well as away from it are overwhelmingly important. The group of physical chemists at the University of Colorado are open to sharing ideas about science and the scientific enterprise: they have and continue to make a difference. My own insights owe an additional debt of gratitude to my colleagues in fields other than my own as well as my fellow fellows at the Radcliffe Institute for Advanced Study at Harvard who inspired seemingly unconnected ideas to come together in unexpected ways. Marie Ferguson, since the mid 1980s, provided advice, unwavering support and friendship. Many thanks to the guest editors and contributors to this festshrift issue of The Journal of Physical Chemistry: I am greatly honored. My accomplishments are my children, Katherine and Paul, my students, collaborators, co-workers, and friends and the new scientific ideas I have contributed and hope to contribute 1166
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