Electronic Nonadiabaticity in Chemical Dynamics

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Millard H. Alexander of The University of Maryland at College Park and Paul J. Dagdigian of Johns Hopkins University are supported by the Experimental Physical Chemistry Program to continue their collaborative studies of the dynamics of nonreactive collisions involving diatomic free radicals, with an emphasis on electronically nonadiabatic processes. They will study weakly bound complexes of the radicals and the predissociation of these complexes in order to gain further information on the underlying potential energy surfaces. The theoretical effort involves development and application of new methods for elucidating the mechanism of molecular collisions and photodissociation, ab initio calculation of the potential energy surfaces and nonadiabatic coupling matrix elements, and full quantum calculations of cross sections and rate constants and the determination of bend-stretch levels of weakly-bound complexes. The experimental effort involves the determination of state-to-state inelastic cross sections for energy transfer processes and the spectroscopy and dynamics of rare gas-diatomic van der Waals complexes. The dominant theme of their research is the influence of electronic angular momentum and/or spin on inelastic energy transfer and photodissociation. During a collision, or during the breakup of a molecule, the internal electronic angular momenta will couple with the motion of the nuclei and hence influence product branching ratios and inelastic propensities. Therefore, a thorough understanding of this coupling mechanism should ultimately lead to a better understanding of how to optimize the desired products in chemical reactions.