MATRIX-CONTROLLED PHOTOCHEMISTRY OF BENZENE AND PYRIDINE

Dewar benzene has been shown to be a primary product from the photolysis of benzene in low temperature argon matrices at 253.77 nm. This is the first observation of Dewar benzene production at this wavelength and a mechanism is proposed that involves benzene S1-S2 state mixing induced by the matrix environment. Analogous experiments on the photolysis of pyridine show that the only primary products are isomeric species derived at least in part from a triplet state of pyridine, probably T1. This is the first observation of photochemistry from the T1 state and may be the process responsible for the small values of tau-p and phi-p in pyridine. Analysis of the IR spectral bands points to the main product being Dewar pyridine although other isomers cannot be ruled out. In contrast to the gas phase, no decomposition of pyridine was found in matrices producing compounds such as acrylonitrile, ethyne, and hydrogen cyanide.