NSF Young Investigator: Many Body Approaches for the Study of Photochemical Processes

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John Stanton is supported by an NSF Young Investigator Grant from the Theoretical and Computational Chemistry Program to develop and implement many-body ab initio molecular orbital approaches to the study of photochemical processes. The approach is based on equation-of-motion and Fock space generalizations of the coupled-cluster approximation for electronic ground states. Specific aims of the research include: 1) the theoretical formulation and computational implementation of techniques for calculating reduced density matrices, electronic properties and analytic energy derivatives for final states parameterized by a class of Fock space methods that allow a spin-adapted, size-extensive, many-body treatment of open-shell states; 2) extensions of existing equation-of-motion methodology that will permit application of these methods to the calculation of nonadiabatic processes; and 3) the design of algorithms that will make these theoretical methods applicable to relatively large systems. Photochemistry tends to drive many of the important chain reactions that determine the complex chemistry of the stratosphere, as absorption of solar photons typically leads to photodissociation. Of current importance is the photolysis and subsequent photofragment chemistry of chlorine containing compounds, as these systems have unambiguously been implicated in catalytic mechanisms leading to destruction of ozone in polar stratospheric regions. Stanton's studies of excited states of these open-shell molecules will assist in their theoretical characterization and detection by spectroscopic techniques. His research will also contribute to the calculation of potential energy surfaces for excited states which can be used to simulate photodissociation events