Special Issue Preface pubs.acs.org/JPCA
A Tribute to Lawrence B. Harding, Joe V. Michael, and Albert F. Wagner for Their 100 Years of Combustion Kinetics Studies at Argonne Energy. At this time, Al Wagner, who had been instrumental in hiring Thom Dunning, was already a member of the Theoretical Chemistry Group, and in 1979, Larry Harding was one of the group’s first new hires to embark on this program. Thom’s second major management decision was to expand the group to include an experimental component to complement the theoretical effort. In 1987, three experimentalists were added to the group to jump-start this effort: Kopin Liu, R. Glen Macdonald, and Joe Michael. Joe’s goal was to develop a shock tube for high-temperature studies of the kinetics of combustion reactions. Remarkably, although Joe built up this shock tube from scratch, he generated and published his first data within a year. Perhaps even more telling, Joe quickly teamed up with Al for a joint experimental and theoretical study of the reaction of O + C2H2 that was published in 1990. The ball was rolling! The most definitive description of the kinetics for a given chemical reaction generally comes from a close collaboration between theory and experiment, and since these early days, such close collaborations have been a hallmark of the Argonne combustion kinetics efforts. Indeed, 20 published papers describe some form of collaboration between Joe and either Al or Larry, or in many instances both of them. These collaborations have contributed to our understanding of many of the foundational reactions of both combustion oxidation and pollutant formation and removal. Most recently, for example, these collaborations have provided the first demonstration of the role of the roaming radical mechanism in thermal kinetics. Of course, in addition to these internal collaborations, Larry, Joe, and Al have also collaborated with a large number of researchers worldwide in the development of theoretically wellfounded descriptions that accurately reproduce high-level experimental data for the kinetics and dynamics of a wide variety of other core reactions of combustion. As all of their collaborators know, Larry, Joe, and Al take great pride in developing a description of the kinetics that accurately treats the key physical aspects of the dynamics, and that is quantitatively correct. Theoretical chemical kinetics currently plays an important role in the development of chemical mechanisms for combustion, providing rate estimates for a great variety of experimentally unstudied reactions and improving the representation of the kinetics for other, more well studied, reactions. These estimates are generally obtained from ab initio electronic structure theory based implementations of transition state theory (AITST) and it is now commonplace for a
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t is with immense pleasure that we acknowledge the seminal contributions to combustion kinetics made by Lawrence Harding, Joe Michael, and Albert Wagner during their combined 100 years of combustion kinetics research at Argonne National Laboratory. Our ability to model and predict the chemistry of combustion has advanced dramatically over the last 40 years. During this time, chemical models for combustion have progressed from simple mechanisms for hydrogen combustion that include only 20−30 reactions, to complex mechanisms for biofuel combustion that include tens of thousands of reactions. Nowadays, such mechanisms not only describe the primary oxidation processes but also can include detailed submechanisms for pollutant formation and removal. The current detailed and quantitative understanding of the great variety of chemical processes occurring in various combustion environments was built upon careful studies of the kinetics and dynamics of an enormous number of individual reactions. Larry, Joe, and Al have played a central role in these advances through the development and application of theoretical and experimental methods to a large number of the key reactions of combustion. Their unassuming nature, in the laboratory and at meetings and conferences, belies their remarkable contributions to the field of gas-phase chemical kinetics and dynamics. The excellent studies reported in the present volume continue to strengthen this important knowledge base. Under the leadership of Thom Dunning, the Theoretical Chemistry Group at Argonne National Laboratory shifted its focus to combustion chemistry in 1978. This shift was motivated by the vision that theoretical chemistry would soon allow the calculation of reaction thermochemistry, rate constants, products, and branching ratios with sufficient accuracy to allow predictive modeling of the reactions relevant to the combustion of hydrocarbon fuels. This shift coincided with the initiation of a new Chemical Physics Program focused on combustion chemistry and directed by Bill Adams within the Office of Basic Energy Sciences at the U.S. Department of © 2015 American Chemical Society
Special Issue: 100 Years of Combustion Kinetics at Argonne: A Festschrift for Lawrence B. Harding, Joe V. Michael, and Albert F. Wagner Published: July 16, 2015 7075
DOI: 10.1021/acs.jpca.5b01917 J. Phys. Chem. A 2015, 119, 7075−7077
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The Journal of Physical Chemistry A
are often a highlight of the combustion and other kinetics meetings. From another perspective, Joe has for many years been one of the top 10 authors cited in the NIST Chemical Kinetics Database. Their list of collaborators looks like a who’s who of gas-phase chemical dynamics and combustion kinetics for the last 40 years. S.J.K. remembers the great joy he had upon receiving the news that Argonne would support him for his sabbatical stay in 1996/1997, as this would afford him with the opportunity to learn from these giants of combustion kinetics. This opportunity for collaboration was also central to S.J.K.’s decision to move from Sandia to Argonne in 2005. Wagner’s research productivity is particularly remarkable when one considers the extent of his administrative duties over the course of his career. Al’s “curse” has long been his effectiveness at providing valuable constructive criticism in a nonthreatening manner; we can recall any number of instances where his suggestions have proven to be remarkably apropos. This ability, together with his willingness to serve as the good soldier, led to his receiving ever greater administrative responsibilities. Fortunately for him and for us, his focus is now back to research. In collaboration with Richard Dawes and Don Thompson, he has developed a novel approach for the generation and fitting of multidimensional potential energy surfaces that can be automated to allow the systematic improvement of the surfaces. Wagner and his collaborators have now applied the approach to both vibrational spectroscopy problems (for example, ground state HCN and singlet CH2) and kinetics problems (for example, the roaming process in the thermal decomposition of dimethyl ether). Recently, he has developed additional interests in semiclassical tunneling and the effect of high gas pressure on the relaxation and reaction of excited molecules. Harding has long been known for his applications of multireference electronic structure methods to the development of global potential energy surfaces. This advanced methodology is central to the description of the novel roaming radical mechanism that he discovered in collaboration with Suits and Bowman. Notably, the term “roaming”, which provides a concise yet physically correct description of a complex chemical phenomena, was invented by Larry as they were preparing their initial paper describing the discovery. Much of Larry’s recent research has focused on further explorations of the roaming phenomenon, with illustrations of its ubiquitous nature, as well as careful studies of the fundamental features of the potential energy surfaces and the development and application of methods for exploring its role in dynamics and kinetics. While Joe has a deep appreciation of the value of the interplay between theory and experiment, he is a champion of the continued importance of experimental chemical kinetics to the combustion research community. In the past few years, the pace of Joe’s research has not flagged, and it is obvious that he still cares deeply about getting things rightand sometimes getting it right takes time. Thus, it was a real pleasure to see Joe and his most recent postdoc, Sebastian Peukert, resolve a problem with the thermal dissociation of ozone that had been bothering Joe since his postdoctoral work with George Kistiakowsky. Joe was really tickled. His deep love of chemical kinetics is conveyed to anyone who talks with him, and his long-term enthusiasm is an inspiration to us all. Of course, none of this work could have been performed without the continued support of the Gas-Phase Chemical Physics Program at the Department of Energy, Office of
mechanism paper to include some application of AITST to a key reaction in the mechanism. Wagner and Harding were pioneers in the development and application of the AITST approach to the study of combustion kinetics. In many of their studies, they formed an exceptional dynamic duo (>20 joint publications), with Larry providing world-class expertise in electronic structure, and Al contributing a deep understanding of transition state theory. Their pioneering AITST studies, which generally include exquisitely detailed explorations of the key aspects of the kinetics as well as numerous methodologic developments, have covered the majority of the most important combustion reactions. Together, Larry and Al’s efforts have been instrumental to the current widespread application of the AITST approach. Larry’s contributions to this effort were recently recognized with the 2014 Bernard Lewis Gold Medal of the Combustion Institute, and Al’s contributions were recognized with a plenary lecture at the Twenty-Ninth International Combustion Symposium in Hokkaido, Japan. This dynamic duo also routinely runs marathons together, with Larry often qualifying for the Boston marathon, whereas, for Al, that goal is gradually becoming a realistic possibility. When it comes to chemical kinetics, however, Joe is the group’s true ultramarathoner: over 50 years in the field and still running. Since his arrival in 1987, Joe has been the leader of the experimental effort in high-temperature combustion kinetics at Argonne. He has demonstrated and characterized the utility of shock-tube measurements in providing high-quality kinetic data for a large number of combustion reactions. In particular, his mastery of atomic resonance absorption spectroscopy (ARAS) and molecular absorption techniques has allowed detailed kinetic measurements at extremely low reagent concentrations. This capability greatly enhances the ability to isolate chemical reactions of interest, and thus extract high-quality rate coefficients with a minimum of modeling. As an example of his work, in 2003, Joe led an experimental effort to record the thermal rate constants for the simplest chemical reaction H + H2 → H2 + H at temperatures between 1100 and 2100 K. By using two combinations of isotopes, Joe and co-workers (Meng-Chih Su and James Sutherland) generated new experimental data that extended earlier investigations over a large range of temperatures. Michael and co-workers then worked with another group of world-class theoreticians (Steven Mielke, Kirk Peterson, David Schwenke, Bruce Garrett, and Don Truhlarall from outside Argonne) to compare their results with those from calculations incorporating the accurate quantum dynamics of the system. For the first time, experimental and theoretical quantum mechanical thermal rate constants agreed perfectly, to within experimental error, for this benchmark chemical reaction, thus providing closure to a 75-year-old scientific problem. This example illustrates several aspects of Joe’s approach to chemical kinetics: his drive for quantitatively accurate chemical kinetic data, his deep appreciation of theory and how it can complement experiment, his ability to use kinetic data to provide insight into dynamical and mechanistic questions, and his willingness to take on big, long-outstanding problems. Due to their unparalleled expertise, Harding, Wagner, and Michael are also highly sought after by external researchers. Indeed, we recall a number of Dynamics of Molecular Collisions meetings where it seemed like every talk was describing a potential energy surface that was developed in collaboration with Larry. Meanwhile, Al’s collaborative studies 7076
DOI: 10.1021/acs.jpca.5b01917 J. Phys. Chem. A 2015, 119, 7075−7077
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The Journal of Physical Chemistry A Science, Office of Basic Energy Sciences (and its predecessors) and, in particular, the Program Officers leading this effort including Bill Adams, Richard Kandel, Bob Marianelli, Allan Laufer, William Kirchoff, Richard Hilderbrandt, Eric Rohlfing, Frank Tully, Michael Casassa, Jeffrey Krause, Wade Sisk, and Mark Pederson. In all their endeavors, Larry, Joe, and Al have played an exemplary role in driving research efforts forward in a productive and yet probing manner that focuses on the key central issues. They continue to serve as role models for young aspiring scientists in the field, and we have all benefited greatly from their efforts.
Stephen J. Klippenstein Stephen T. Pratt
Argonne National Laboratory
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DOI: 10.1021/acs.jpca.5b01917 J. Phys. Chem. A 2015, 119, 7075−7077
