Absorption Spectra and Photochemical Rearrangement of Cycloheptatriene Cation to Toluene Cation in Solid Argon

Article abstract of DOI:10.1021/ja00538a006

The toluene and cycloheptatriene cations have been produced and trapped in solid argon by matrix photoionization techniques.Toluene experiments gave a photosensitive 430-nm absorption and weak 480-nm band, the cycloheptatriene studies yielded a broad 480-nm absorption and a weak 430-nm band; these matrix bands are slightly red shifted the photodissociation spectra (PDS) peaks for the corresponding parent cations.Visible photolysis in cycloheptatriene experiments decreased the 480-nm band and increased the 430-nm absorption, indicating that cycloheptatriene cation can be photochemically rearrnged to toluene cation.The toluene cation absorption bandwidth is more than an order of magnitude less in solid argon than in ICR experiments; this may be due to quenching excess vibrational energy in the ground-state ion by the matrix and / or a reduction in the rate of internal conversion from the excited-state ion in the matrix owing to rapid relaxation to lower vibrational levels of the excited state where the density of states for vibronic coupling is less.The reduced photolysis rate of toluene cation in the matrix is consistent with the latter point and a efficient removal of vibrational energy from the vibrationally excited ground-state ion resulting from internal conversion.