Theoretical Study of Photodissociation Dynamics in the Gaseous and Condensed Phases

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Hua Guo at the University of Toledo is supported by the NSF Theoretical and Computational Chemistry Program for theoretical investigations of chemical reaction dynamics. The concern of this work is the study of photodissociation; in particular, time dependent quantum mechanics will be used to study the photodissociation dynamics of small molecules. These processes will be studied in the gas phase, on surfaces, and in solution. In order to treat problems in the later two cases, a new theoretical procedure will be developed which is a hybrid approach combining quantum and classical methods. With this hybrid approach, the quantum features of the molecular reaction are properly addressed but the effects of the medium, substrate or solvent, are included. For the gas phase studies, a few modest size polyatomic molecules will be treated; these include rare gas complexes and Ryderg excited states of methyl complexes. The dynamics of photo-induced chemistry, in general, and of photodissociation, in particular, depend on the details of the interaction energies among the atoms in the system; i.e., on the details of the potential energy surfaces. However, it is not simple to relate the features of this surface to the identity of the reaction products and to the energy distribution over these products. The studies of photodissociation being carried out in this project will enhance the understanding of the relevant relationships. In particular, two aspects of the work help to insure that it will have considerable impact on this important scientific goal. First, the work is being carried out is close contact and, often, in collaboration with experimentalists. Because of this, the approximations used to obtain the underlying potential energy sufaces as well as those used to study the time dependent quantum features of the reaction can be validated. Second, the systems being studied are carefully chosen to yield important and useful information. They are sufficiently small to be tractable for high accuracy quantum mechanical treatments yet sufficiently large to contain chemical bonds and other features relevant to more general problems in photochemistry.