Unimolecular processes in vibrationally highly excited cycloheptatrienes. II. Steady-state photoisomerization

The steady-state unimolecular photoisomerizations of cycloheptatriene, 7-methyl-cycloheptatriene, and 7-ethyl-cycloheptatriene have been studied at wavelengths between 238 and 289 nm. The reactions proceed via vibrationally highly excited electronic ground state molecules. The specific rate constants k (E) for the unimolecular aromatizations and H-atom shifts are derived and compared with statistical calculations. Absolute values of the average step sizes <ΔE≳ for energy transfer of highly excited molecules are obtained via calibration of Stern–Volmer curves against specific rate constants from thermal isomerization experiments.