Abstract

IR excitation of selected vibrational modes of a variety of molecules trapped in solid rare gases causes a photoisomerization. The reactions are generally single photon processes which involve a rotation about a single bond. The quantum yields for photoisomerization have now been measured in both the forward and re verse directions for several molecules. The range of excitation includes both the fundamental and first overtone vibrations. These quantum yields vary from 0 to 1. The vibrational photochemistry is not consistent with a statistical redistribution of energy in the guest molecule before reaction. The guest molecules are not isolated in a gas phase sense; vibrational energy flow to the lattice competes with reaction and intramolecular (guest) energy redistribution. It is likely that relaxation of the guests can occur via specific pathways. Evidence is presented to show that the products and the quantum yields for their formation depend on the relaxation rates and pathways. It is thus possible to create product distributions by even broadband (nonlaser) IR irradiation that are impossible thermally.

© 1986 Optical Society of America