The Role of Multiple Potential Energy Surfaces in Chemical Reactions and Photodissociation

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Millard Alexander of the University of Maryland at College Park and Paul Dagdigian of Johns Hopkins University are supported by the Experimental Physical Chemistry Program to continue their collaborative studies of the dynamics of chemical reactions and molecular photodissociation, with an emphasis on electronically nonadiabatic processes. The theoretical research involves the development and application of new methodology for the study of molecular collision and dissociation dynamics. The experiments will measure state-resolved electronically and rotationally inelastic cross sections involving open-shell diatomics, with special attention on highly excited rotational levels, photolytically prepared. The project goal is the elucidation of how the interplay between more than one potential energy surface, and the coupling between these, governs the dependence of reaction cross sections and rate constants on the fine-structure levels of the reactants, and product internal state distributions and orientation after collisions or photodissociation. The dominant theme of this project is the influence of electronic angular momentum and/or spin on chemical reactions, inelastic energy transfer and photodissociation. Progress toward full understanding is achieved by investigation of a few exemplary systems, with theory and experiment in close collaboration. Radicals are atomic and molecular species that have unpaired electron spins. This property leads them to be chemically reactive, and in fact radical reactions underlie all of chemical kinetics. Collisions that involve radicals, as well as light-induced dissociation that leads to radical fragments, are complex processes whose description is inherently quantum mechanical. This effort seeks to achieve fundamental understanding of radical reaction systems with the goal of improving overall knowledge of chemical reaction dynamics and kinetics.