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

Abstract

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.

Ultraviolet Photoelectron Spectroscopy of Some C7H7- Isomers: Quadricyclanide, Norbornadienide, Cycloheptatrienide, and 1,6-Heptadiynide

“…Investigations into the properties of cycloheptatriene have included vibrational spectroscopy of the solid, electron spin resonance matrix study of the radical cation, resonance Raman study in solution of the (1,7)-hydrogen shift in cycloheptatriene, , and several investigations − into the isomerization of cycloheptatriene to toluene. These studies start with the original observation 42 in 1962 that photoisomerization of cycloheptatriene at low pressures produces toluene, most likely by formation of an excited singlet state which converts to an excited vibration of the ground electronic state before collisional isomerization to toluene.…”

Vibrational energy flow within excited electronic states of large molecules

“…Moreover, such AE values are sensitive to modeling, probably more so than in the sophisticated uses of chemical activation and photoisomerization studies that have been so successful for ground electronic states. 34,35 This liability is illustrated in the benzene experiments discussed below.…”

High Temperature Ultraviolet Absorption Spectra of Polyatomic Molecules in Shock Waves

“…The room temperature absorption coefficients were measured in separate experiments in a Cary 17 D spectrometer with simultaneous pressure control by a Setra capacitance manometer, see also Ref. [12]. The used substances were of highest available commercial quality.…”