Gas-Phase Chemical Dynamics
Selected experimental and theoretical results in elementary combustion kinetics. Clockwise from the upper left, the images correspond to the following: the reaction rate for H2 + O2 → HO2 + H, where the symbols indicate various experimental results, and the solid line is the theoretical prediction; a schematic diagram showing the calculated energies of the key points on the O + HCCH potential surface; the time-dependent H atom concentrations determined from the shock tube decomposition of acetaldehyde; and the flash or laser photolysis shock tube apparatus in the laboratory of Joe Michael. The background image shows the interaction potential between a rigid methyl (CH3) radical and a rigid HCO radical separated by a distance of 6.8 au (corresponding to the geometry of the roaming saddle point). This montage was on the cover of a special issue of the Journal of Physical Chemistry A in honor of Lawrence Harding, Albert Wagner, and Joe Michael, and their combined 100 years of Chemical Kinetics research at Argonne. J. Phys. Chem. A 119, 7075 - 7950 (2015): http://pubs.acs.org/toc/jpcafh/119/28
The Gas-Phase Chemical Dynamics (GPCD) group uses complementary theoretical and experimental methods to explore and determine the thermochemistry, dynamics, and kinetics of gas-phase chemical processes, with a principal focus on the chemistry of combustion.
Our goal is to develop a fundamental understanding of gas-phase chemistry, with an emphasis on the elementary chemical reactions, non-reactive energy transfer processes, and coupled kinetics processes involved in combustion. This understanding will ultimately provide the foundation for the predictive modeling of a range of combustion devices, as well as strengthen the foundations of other areas of gas-phase chemistry, including atmospheric chemistry and the chemistry of low-temperature plasmas.
Our approach combines a theoretical effort in the energetics, dynamics, and kinetics of chemical reactions with an experimental effort in thermochemistry, dynamics, and kinetics under both chemically isolated conditions and more complex conditions. The group's members maintain expertise balanced among theory, experiment, and modeling.
The theoretical effort involves both large-scale applications of existing methods and the development of new theoretical methods. Electronic structure techniques that determine intermolecular forces, dynamics techniques that determine molecular responses to these forces, and kinetics techniques to determine the rates of the resulting reactions are all being pursued. Modeling of more complex combustion environments involving coupled kinetics and transport is also being developed, along with approaches for global uncertainty and sensitivity analyses.
The experimental effort includes flow tube studies across a broad temperature range, thermal reaction kinetics measurements in shock tubes at high temperatures, state- and angle-resolved photoionization and photodissociation measurements, and chirped-pulse millimeter- and microwave studies of molecules in reactive environments. Reaction rates, branching ratios, product distributions, and ion-cycles for thermochemical determinations are all being examined. Increasingly, the group is developing rational approaches to problem selection, for example, through sensitivity analysis of chemical kinetic models, and through network-based analysis of thermochemical data. The group's greatest asset is the synergy that results from the strong interactions among group members and between the theoretical and experimental efforts.
We frequently collaborate with the Combustion Chemistry Group at the Combustion Research Facility at Sandia National Laboratory in Livermore, CA.