MATRIX PHOTOCHEMISTRY OF CYCLOHEPTATRIENE - SITE EFFECTS

An experimental study of CHT photolysis at 2537 Angstrom in argon and nitrogen (N-2) matrices is presented. The sole IR detectable product i s identified as BCHD: bicyclo[3.2.0]hepta-2,6-diene. It is found that CHT molecules trapped in spectroscopically distinct sites were convert ed to the product at different rates. In the initial stages of the pho tolysis, the population of some CHT trapping sites increased, indicati ng site population transfer. In the long run, however, all sites were depleted. Molecular dynamics simulations are performed to estimate the structure of the different sites, and together with a kinetic model, are used to account for the UV induced changes. A tentative energy lev el diagram of the system is offered, in an attempt to rationalize the total absence of toluene which is formed predominantly in the gas-phas e irradiation of CHT at this wavelength. The ''twin state'' concept is instrumental in this rationalization.