Professor John H. Frederick at the Chemistry Department of the University of Nevada, Reno is supported by a grant from the Theoretical and Computational Chemistry Program at NSF to study vibrational spectroscopy and excited state molecular dynamics. The work supported under this grant is focussed on light induced reactions that form isomers, different stable geometries, in several gas phase molecules. The molecules that are being studied are representative of a class of molecules which have conjugated pi-systems. The first step in the studies is to use a combination of experimental data and ab initio theoretical data to construct descriptions of the interaction energy surfaces. Then, the dynamics of excitation from the ground to the first excited state and de-excitation back to the ground state are studied using both quasiclassical and quantum mechanical methods. These studies may lead to methods to control the way in which the reactions proceed and the amounts of different isomers which are formed. The photochemistry of molecules with conjugated pi-systems is of central importance for many natural processes, such as vision and photosynthesis, and for organic conductors. Many molecules in this class have been extensively studied by experimentalists and by theorists and much is known about the properties of these systems. However, the dynamical mechanisms by which photochemical transformations occur are still not fully understood. The work under this grant is addressing this missing link.
