With funding from the Organic Dynamics Program of the Chemistry Division, Professor Howard E. Zimmerman of the University of Wisconsin - Madison will study mechanistic fundamentals of organic photochemistry, via computational approaches to understanding of hypersurfaces and radiationless processes, and computationally supported systematic approaches to solid state photochemistry. The project includes examination of ways to predict the ability of alternative transition structures to fit in reactant crystal lattices (i.e. ways to determine what products are viable in solid state photoreactions), studies of whether barriers on excited hypersurfaces or radiationless decay processes control photoproduct formation in certain specific instances, and a study of polymer matrices as constraints on molecular photochemistry. The phase in which a chemical reaction is conducted - crystal, amorphous solid, liquid, or gas - can determine the outcome of the reaction. Crystal constraints are frequently very great but are not usually readily predictable. This work will develop a way of prediction of favored reaction pathways for light-induced reactions in crystals using computational techniques. Other computational techniques will allow understanding of details of reactions in less constrained environments