Unimolecular processes in vibrationally highly excited cycloheptatrienes. III. Direct k (E) measurements after laser excitation

Abstract

Vibrationally highly excited substituted cycloheptatrienes in their electronic ground states have been prepared by single photon UV laser excitation and subsequent internal conversion. The unimolecular isomerizations of these species have been followed by time resolved UV absorption spectroscopy. The specific rate constants k (E) could be obtained directly at low pressures for methyl‐, ethyl‐, and isopropyl‐substituted cycloheptatrienes. The influence of collisions on the rate of product formation has been elucidated as well. The results are compared with thermal and steady‐state photoisomerization experiments. Statistical theories of unimolecular reactions can fully account for all results.