Theoretical Studies of Electronic Structure and Dynamical Aspects of Electronically Nonadiabatic Processes

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This project, supported by the NSF Theoretical and Computational Chemistry Program, develops computational methods for the study of Born Oppenheimer breakdown in excited electronic states, and their application to the study of photochemical pathways. Methods using analytic energy derivatives for multiconfiguration self-consistent field (MCSCF) wavefunctions are employed to locate low energy surface crossings and avoided crossings. The theory is applied to the study of spin-forbidden, non-adiabatic processes relevant to gas lasers and atmospheric chemistry such as photodissociation of ozone, at wavelengths below 310 nm, to produce both singlet and triplet products. The central goal of this research is the development of the quantum mechanical theory of elementary chemical reactions of molecules in electronically excited states, usually resulting from the absorption of light of an appropriate frequency. An important feature of these photochemical reactions is the fact that these excited molecules can jump from one electronic state to another with a concomitant transfer of energy between electronic, vibrational, and translational degrees of freedom. This theoretical research project provides deeper insight into such molecular processes revealed by spectroscopic and kinetic experiments. This project develops basic theoretical tools widely applicable to photochemical processes, in particular, to computer models of ozone depletion in the atmosphere.