J. Phys. Chem. B 2008, 112, 191-194
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Autobiography of James T. (Casey) Hynes I was born in October, 1943 in Miami Beach, Florida, where my father was in the Army Air Force Officer’s Training School, and shortly thereafter I acquired my nickname. My father had left for Europe a bit before I was born, and his first vision of his son was a canonical baby photo of me, scantily attired in a baseball cap. Thinking of a then famous folk figure, Casey at the Bat, he dubbed me “Casey”, a nickname which has stuck, sometimes to the confusion of others. (For example, in the 1980s when I was working both on reactions in solution and gas phase intramolecular energy flow, there were some who thought that it was Casey who did the former and some other fellow James T. who did the latter.) Soon thereafter, my mother moved back to Washington, D.C., the home of both she and my father. My parents were of IrishScotch and Irish heritage, respectively (and I especially recall the lilting accents of my Irish great aunts). Our family was what I would term lower middle class. But despite, or perhaps more correctly because of this, I was extremely well educated in Washington area schools, most notably on scholarship at St. John’s, a high school located in downtown D.C., where I came to appreciate the racial mix so characteristic of the area and acquired a life-long addiction to black vocal group harmony. I was attracted to Chemistry and even succeeded in exploding hydrogen in my face in my basement “lab”, resulting in a day in the hospital. While this could have been reasonably interpreted as an early signal that theoretical, rather than experimental, chemistry was for me, in fact the competing area issuing its siren call was English (and other) Literature. This intellectual schizophrenia continued at Catholic University in D.C. to which I was fortunate to win a scholarship. For the first 2.5 years, I followed a path for which I could remain free to finally commit either to Chemistry or to English Literature. Ultimately, two brilliant third year courses decided me for the former: Organic, taught by John Eisch in a very “physical organic” fashion, and Physical, taught by Gilbert Castellan from the proofs of his soon-to-be-published textbook. (Years later, I could partially repay the latter debt by writing several hundred “thought” questions for the third edition of that text.) Further, I decided that I wanted to do theoretical chemistry, so I had to quickly teach myself mathematics. Previously, I had not liked math and indeed had never done very well in it, mainly because I had always been afraid of it. Once the fear was overcome, catalyzed by seeing what it could do in Chemistry, the skill in math came fairly easily. I also worked in Robert Moriarty’s laboratory as an NSF Undergraduate Fellow, attempting without spectacular success to theoretically interpret the UV spectra of some mesoionic compounds in solution. Professor Moriarty had come from Princeton, and it was he who pushed me in that direction for graduate school. I went to Princeton intending to do theory with Walter Kauzmann, only to learn that he had become chairman and was not accepting any students. Arthur Tobolsky offered me the opportunity to do polymer statistical mechanics, so I joined his group. Unfortunately, I did not find this very satisfying, and when I learned that John Deutch, who at that time was in D.C. at the National Bureau of Standards on a postdoc with Bob Zwanzig, would join the faculty the fall of 1966, I arranged to spend the summer in D.C. and approach him about joining his as yet nonexistent group. In what I later recognized to be a very
courageous act, John accepted me on the basis of what, to quote Winston Churchill on his entrance exam for Harrow, were fairly “slender indications of scholarship”. The physical chemistry grad students at Princeton were a very gifted and convivial lot: besides Bob Cukier and Claude Cohen, there were my best friend Ed Samulski (who taught me about Johann Sebastian Bach and Paul Ce´zanne), Chuck Kolb, Peter Kollman, and Ray Kapral, among others. The Deutch group was at first myself and Bob, joined later by Claude. Our group seminars were held together with Zoltan Soos’ group. I remember them vividly as intellectually stimulating, albeit emotionally harrowing; at all events, we were forever after well prepared for the real academic world. My thesis topic was the development of the Wigner equivalent formalism for determining quantum corrections for classical time correlation functions. John was a terrific advisor, dealing out in equal portions intensity, stimulation, education, and personal concern. On the personal side, this was a happy time. My college sweetheart Judith Roy and I were married, and our two daughters Michelle and Lauren were born. Decades later we divorced, but we have remained close friends, taking delight and pride in our exceptional daughters. My next stop was an NIH postdoctoral fellowship with Irwin Oppenheim at MIT. Theoretical chemistry at MIT in 1970 was extremely exciting. All of the students of Irwin, John Deutch (had transferred from Princeton), Bob Silbey, and John Ross, an incredible collection of talent, were packed together in the theory complex (aka the “dungeon”) with an unbeatable atmosphere of interaction and stimulation. While it transpired that Irwin and I did not publish anything from this period, I took away from MIT the lasting memory of him as a powerful and incisive intellect coupled with a warm and caring heart. I pause, gentle reader and most especially gentle students and collaborators, to say that in the following I will not be able to name all the students and collaborators involved in the research that I will sketch; their names are to be found in a list in this issue. Nor will I use well-deserved adjectives such as gifted, brilliant, talented, etc. to characterize the ones I do name. In an earlier version of this essay, I attempted this, but my powers as a thesaurus were insufficient to avoid an annoying repetitiveness that seemed to me almost to nullify the praise I wished to give. So, let it be taken as read that I have great admiration for them all, a point to which I return at the conclusion. In fact, my stay at MIT had been cut short by the lucky event of being hired at the University of Colorado, Boulder, where I started in January 1971. Coming from the theoretical hothouse of MIT to Boulder was a bit of a culture shock, and I well recall the many times that I would talk out loud to myself about theoretical problems. But the situation soon brightened considerably with the arrival of my first Ph.D. student Scott Northrup, and we started working on chemical reactions in solution. The inspiration for this research direction was the fact that I had always found reactions the most interesting thing in chemistry. A second important development of these early years came with a collaboration with two other ex-denizens of the MIT theory dungeon: Mike Weinberg and Ray Kapral. This eventually turned into constructing microscopic boundary conditions for hydrodynamic flow fields in connection with molecular rotation and translation. Our conclusion that molecular collisions and
10.1021/jp710517n CCC: $40.75 © 2008 American Chemical Society Published on Web 01/10/2008
192 J. Phys. Chem. B, Vol. 112, No. 2, 2008 hydrodynamic flow were simultaneously important came at a time when there was a strong prevailing view that there were no significant molecular aspects for these motions and that hydrodynamics was the entire story. A powerful impetus for accelerating our solution reaction research came from the seminal picosecond experiment on iodine recombination by Ken Eisenthal; this was the clearest possible signal that now was the time to get serious about reactions. Our own next important steps on the solution reaction front came with the 1980 development of the Stable States Picture (SSP) with Scott Northrup and what is now termed Grote-Hynes (GH) theory for the rate constant with graduate student Rick Grote, using the SSP. The idea for GH theory came from what I call a “Curious Incident of the Dog in the NightTime” effect, after the incident in the Sherlock Holmes story “Silver Blaze”, to which I refer the reader for the allusion’s explication. Briefly, the standard and pioneering Kramers theory would suggest that a surrounding solid would put a stop to all chemical reactions, but it does not. Incorporation of the typically very short time scale when the reaction system crosses the Transition State (missing in Kramers theory) led to GH theory, which is now a highly successful and “standard” theory; more of that anon. A bit later, postdoc Gert van der Zwan and I used GH theory to describe the influence on a rate constant of nonequilibrium solvation, the feature that the solvent’s electrical nuclear polarization could be out of equilibrium with the evolving charge distribution in a reaction system. In a subsequent study, we showed that in special cases GH theory could be turned into Transition State Theory by defining a new coordinate. Our first essay into the theory of time-dependent fluorescence and solvation dynamics was also with Gert. In this same early to mid 1980s period, two important new research threads began: vibrational energy transfer in solution and intramolecular energy flow in highly vibrationally excited molecules. In the first arena, the key was David Nesbitt, a graduate student doing theory with me and experiment with my colleague Steve Leone. We examined the vibrational relaxation of newly recombined, highly vibrationally excited molecular iodine in solution and showed that this explained the celebrated Eisenthal experiment mentioned above. In the second arena, the keys were graduate student Ned Sibert and postdocs John Hutchinson and Turgay Uzer, all shared with my colleague Bill Reinhardt. Two of the numerous exciting results from this research with this group were a molecular level description of the linewidths of the CH overtones in benzene observed experimentally in the gas phase by Michael Berry and a mechanism for the gas phase overtone-induced photodissociation of hydrogen peroxide, experimentally observed by Fleming Crim. The period described in the last two paragraphs saw the solidification of various already nascent aspects of my scientific perspective: I changed to thinking of myself as a Physical Chemist doing theory rather than as a Statistical Mechanician. I concluded that a knowledge of gas-phase dynamics was just as important as knowledge of solvent dynamics to understand anything that was going on in solution. I concluded that theory needed to be coupled to experiment, even if only indirectly, to be relevant. Perhaps most importantly, I came to appreciate that one had to “think like a molecule” to make real progress. My first involvement with computer simulation came in the mid- to late 1980s as the result of involvement in and co-organization of various CECAM workshops in Orsay on reactions in solution. Key players here were Giovanni Ciccotti and Ray Kapral, and we collaborated then and later on
simulations of several relatively simple reactions. The plunge into simulations of reactions involving bond-breaking and -making and simultaneous electronic rearrangement came with an extended collaboration with Kent Wilson and his students on a model atom transfer, but most especially on the Cl- + CH3Cl SN2 reaction in water, whose free energetics had been worked out by Bill Jorgensen. The agreement with GH theory was amazingly good, not only for the case we thought was the most realistic but also for a number of force field variations. Beyond that, the analytic models for what the reaction coordinate was, and what solvent barriers were, in the transition state region worked just as well. While I had thought that GH theory had the right idea, I had never expected it to be as quantitatively accurate as it proved to be in this and many other subsequent simulation studies, a number of which we performed. But I think that it was these SN2 studies and the theoretical/experimental work of Biman Bagchi, David Oxtoby and Graham Fleming on isomerization kinetics that really put GH theory on the map. With some exceptions, GH theory typically predicts that Transition State Theory (TST) will be an excellent approximation to within a factor of 2 for the rate constant let us say (whereas Kramers theory would predict large to very large discrepancies). My view is that GH theory shows why TST should typically be a very good approximation. Most chemical reaction barriers are sharp so that there is very little time for a solvent or any other environment to exert much effective dynamic friction on the reaction coordinate in the transition state region. The Cl-/CH3Cl system provided the background for two other studies with Kent and his group. The first followed in detail the reaction path from reactants to product, showing the timing and extent of the vibrational excitation of the reactant CH3Cl, of the solvent rearrangement, of the charge flow in the system, and of the bond rearrangements. The second analyzed the vibrational de-excitation of vibrationally hot CH3Cl in water, showing the dramatic effect of Coulombic interactions. But our solution reaction work so far had several key lacunae remaining to be addressed. Clearly bond-breaking and -making reactions required quantum chemistry for their treatment. And what could one say about general reaction paths? And what about reactions such as proton transfer where quantization of the nuclear coordinate must be important? And how could one learn more about and characterize the solvent dynamics that would influence the dynamic friction? We began to address these issues in an analytic fashion in the late 1980s to early 1990s together with several postdocs. For the first topic, with Hyung Kim we used a simple valence bond approachspioneered in a chemical context by such masters as Coulson, Mulliken, and Jortner and in a computational context by Arieh Warshels to deal with quantum chemistry in solution, an approach we have used ever since. Perhaps the most interesting “chemical” result in this period was our argument that the standard physical organic chemistry explanation for solvent effects on SN1 unimolecular reactions such as the tertbutyl chloride dissociation needed to be replaced with an alternate view. For the reaction path issue, Sangyoub Lee and I derived an analytic solution-phase generalization of the Fukui intrinsic reaction coordinate, which was subsequently used in the group for a variety of reactions, e.g., the SN1 dissociation and the I2- vibrational relaxation/recombination problem. The proton transfer work really started in earnest with the arrival of Daniel Borgis. We focused on the analytic treatment of the rate constant both for the tunneling (nonadiabatic) regime and for the quantized over the barrier motion (adiabatic) regime and
J. Phys. Chem. B, Vol. 112, No. 2, 2008 193 emphasized the key role of the proton quantization, the identity of the solvent rather than the proton as the reaction coordinate, and the crucial role of the hydrogen bond coordinate in the tunneling regime. Some years later, my Boulder colleague Kevin Peters put experimental flesh on these theoretical bones, not only for proton transfers but also for other reactions for which we had developed theories. On the solvation dynamics front, perhaps the most important development was the demonstration with Emily Carter that the initial inertial Gaussian time dependence was very important in determining a surprisingly large portion of the dynamics, discovered about the same time by Mark Maroncelli. This period also saw one of my occasional forays into methodology, the development of the “Blue Moon” Ensemble, with Emily, Giovanni Ciccotti, and Ray Kapral; this has proved to be a convenient and powerful method for dynamical simulations with a constraint present. Finally, by this time I had lost interest in GH theory, except for a few adventures into some new and different areas, such as electron-hole pair friction effects for electron transfer at electrodes with Barton Smith and ionic atmosphere friction effects for charge-transfer reactions with former postdoc Gert van der Zwan. These years also brought tragedy: the loss of my wife Teresa Fonseca, who died in December 1991. There are no words to express the magnitude of that loss. One may read something about Teresa and her spirit and courage in the 1994 Journal of Molecular Liquids Memorial issue for her. Before her worsening illness stopped her, Teresa had made much progress in understanding and formulating a theoretical description for the ever-vexed issue of the dynamics of the famous Twisted Intramolecular Charge Transfer (TICT) molecule DMABN. Hyung Kim and I finished her work for her as best we could. Teresa took great pride in her work and would have been pleased to see that description confirmed several years later in experiments by my future French colleagues Pascale Changenet, Pascal Plaza, and Monique Martin, together with Yves Meyer. The mid- to late 1990s saw a return to some earlier topics but in different directions, as well as several completely new thrusts and a new position. Motivated by the pioneering picosecond infrared experiments of Alfred Lauberau and with the aid of three postdocs, we again took up vibrational energy transfer, but now for hydrogen (H)-bonded systems: in Hbonded complexes with Peggy Bruehl, vibrational predissociation in such complexes with Arnulf Staib, and for HOD in liquid D20 with Rossend Rey. In the 21st century, the experimental technology improved considerably and the last topic was taken up again in outstanding work by Jim Skinner. We also now undertook detailed simulations, complete with quantum chemical input and quantization of the proton motion, of the acid dissociations of HCl and HF in water with postdoc Koji Ando. Among the insights gleaned were a microscopic picture of the water rearrangements serving as the reaction coordinate and that the Mulliken charge-transfer picture was a correct description of the electronic rearrangements accompanying the proton transfer. Stimulated by discussions with Boulder colleagues “Ravi” Ravishankara, Steve George, and Maggie Tolbert, postdoc Brad Gertner and I began to examine heterogeneous reactions on ice surfaces important for the stratospheric Ozone Hole, focusing on the mechanism of the HCl ionization, This was followed by investigations with postdoc (and now senior collaborator) Roberto Bianco on the mechanisms of the two key reactions involving chlorine nitrate ClONO2, the first being its hydrolysis and the second being its reaction with HCl to produce molecular chlorine as one of the products. These showed that the ice was
an active chemical participant, providing a proton-transfer chain, rather than just acting as a platform and solvating agent. It is almost as if the ice were acting like an enzyme. But by far the most important event of the mid to late 1990s was my being brought back to real life by my partner Thu-Hoa (“2wa”) Tran-Thi, a CNRS researcher in Saclay and - more to the point - a very special person. We have been very happy together and that says it all. In October 1999, I had accepted a CNRS position at the Ecole Normale Supe´rieure in Paris and resigned half my position at Boulder. Beyond obvious personal motivations (here read 2wa), I was professionally attracted by the opportunity to begin new problems, first among them the theoretical characterization of the nonlinear optics of push-pull polyenes with then ENS colleague Mireille Blanchard-Desce and postdoc Ward Thompson and later also with my first ENS grad student Damien Laage and ENS colleagues Monique Martin and Pascal Plaza. The 21st century has seen some exciting new directions in my bimodal Boulder and Paris scientific life. In another foray into methodology, this time motivated by our heterogeneous atmospheric chemistry work, postdoc Akihiro Morita and I developed a simulation technique to calculate the surfacesensitive Sum Frequency Generation spectrum and applied it to the water surface. With postdoc Phil Kiefer, we significantly extended the group’s previous proton-transfer efforts to the derivation of activation free energy-reaction free energy relationships and kinetic isotope effects (KIEs), the most frequently experimentally measured characteristics of proton-transfer reactions. We could show for example that the KIE behavior thought to support the most established view in which the proton is the reaction coordinate in fact also followed from the quantum proton/solvent reaction coordinate description, and several ways to distinguish between the strongly contrasting perspectives were identified. In fact, many experiments on proton transfer are actually carried out in the excited electronic state. With 2wa, Philippe Millie´, and postdoc Giovanni Granucci, we could show that the marked enhancement of the acidity of a photoacid compared to the ground state acid was not due to a chargetransfer effect on the acid side, as in the long held popular view, but instead arose from an effect on the product, photobase side. My Boulder colleague Josef Michl had much to do with bringing conical intersections (CIs) to the fore in the photochemical community. Strangely enough, our own involvement with these “photochemical funnels” commenced with a ground electronic state reaction and began with a suggestion of my ENS colleague Christian Amatore. With Damien Laage and ENS colleague Irene Burghardt, we showed that the activation free energy for and the dissociation pathway of a radical anion such as chlorobenzene radial anion in solution critically involved the avoidance of a CI by bending of the bond to the departing anion, here the chloride ion. Irene and I (initially also with Lorenz Cederbaum and later joined by postdoc Riccardo Spezia) next turned to the photochemical CI problem, focusing on the influence of a polar environment on the geometry, reaction paths, and dynamics for a CI involving charge transfer. It is a pleasure to record that our theory revealing some very striking effects here was based in part on an extension of an early electronic structure model due to Josef and his co-workers. We returned to water dynamics but now in several new directions, inspired by the ultrafast infrared experiments that were coming thick and fast. First, Rossend Rey, postdoc Klaus Moller, and I showed that the dephasing of the OH vibration for HOD in D2O was governed by the breaking and making of H bonds, a conclusion also reached in Jim Skinner’s group. With
194 J. Phys. Chem. B, Vol. 112, No. 2, 2008 (now CNRS colleague) Damien Laage leading the way, we demonstrated that the reorientation of a water molecule in water should not be viewed as diffusional but rather as involving large jumps, induced by rearrangement in the molecules’ first and second hydration shells, a conclusion also reached for the reorientation of a water in the first hydration shell of the chloride ion. The icing on the cake is that analytic formulas can describe the resulting reorientation times! Our atmospheric work also took on new colors. Shifting away from the chlorine-based heterogeneous reactions mentioned above, Roberto Bianco, grad student Shuzhi Wang, and I looked at the acid dissociation of sulfuric acid and then of nitric acid at an aqueous surface. Remarkably, these well-known strong acids (in dilute aqueous solution) here act as weak ones, a conclusion important for reactions on aerosols in assorted regions of the atmosphere. Stretching the definition of atmosphere quite a bit, ex-postdoc Gilles Pelsherbe and postdocs Celine Toubin, Sichuan Xu, and Denise Koch, and I also looked at the fascinating question of whether an amino acid could be produced by reactions on icy grain mantle particles in the (very cold!) Interstellar Medium. The jury is still out, but we have already succeeded in showing that the penultimate step in a Strecker synthesis route to glycine is possible, via a proton relay similar to that found previously for the chlorine heterogeneous chemistry. From time to time, we have even ventured into the fascinating world of clusters. A first example is the photodissociation of NaI in small water clusters, a paradigm electronic curve crossing problem, motivated by discussions with Ahmed Zewail. Branka Ladanyi, joint postdoc Gilles Peslherbe, and I had hoped to see a clear illustration of Marcus inverted regime electron transfer, but this turned out to be thwarted by water evaporation from the cluster. The second example was inspired by discussions with Mark Johnson. Ward Thompson and I applied the Mulliken
charge-transfer (CT) picture, which had proved to be correct for solution-phase proton transfer, to Mark’s experiments on the OH vibrational redshift for halide ion-water dimers and found that increasing CT indeed played a key role in increasing the redshift. Mark and Ken Jordan (another ex-denizen of the MIT theory dungeon) subsequently did a beautiful experimental/ theoretical study on a particular anion in which CT is suppressed by spin issues and showed that the redshift was less than that expected on the basis of all the other ion properties. Finally, there has even been a resurgence of my interest in GH theory, but now for enzymes. With Inaki Tunon and Vicente Moliner and their students, we showed that the theory worked quite well, but more importantly that it could be used to understand and quantify key aspects of the murky issue of dynamical effects on the catalysis. I find these biochemical problems fascinating, and several challenging ones are underway, including the determination of the mechanisms of the intercalation of anticancer drugs into DNA and of peptide bond formation in vivo. Long ago my distinguished Boulder colleague Stan Cristol remarked that “The function of theory is to teach us how to think”, a sage precept that I have attempted to highlight in my own efforts. The science done so far has all been a wonderful ride, and I hope that it will continue apace. In closing, I thank my good friends Ned, Todd, and Irene for arranging this special issue. It only remains for me to express my admiration and gratitude to my students and collaborators for their marvelous contributions, to my colleagues in Boulder, Paris, and around the globe for their stimulation and friendship, and most especially to the women in my life who have enriched it beyond measure.
James T. (Casey) Hynes
