Hydrogen Atom Loss from the Benzene Cation. Why Is the Kinetic Energy Release so Large?

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Vol. 110; no. 27; pp. 8519 - 8527
• Main Authors: Gridelet, E, Lorquet, A. J, Locht, R, Lorquet, J. C, Leyh, B
• Format: Journal Article Web Resource
• Language: English
• Published: United States American Chemical Society 13.07.2006; Amer Chemical Soc
• Subjects: C6H6; Chemistry; Chimie; H-loss from Benzene cation; Kinetic energy release distribution; Maximum entropy method; OTST theory; Physical, chemical, mathematical & earth Sciences; Physique, chimie, mathématiques & sciences de la terre; SACM model
• ISSN: 1089-5639; 1520-5215; 1520-5215
• DOI: 10.1021/jp056119h

The kinetic energy release distributions (KERDs) associated with the hydrogen loss from the benzene cation and the deuterium loss from the perdeuteriobenzene cation have been remeasured on the metastable time scale and analyzed by the maximum entropy method. The experimental kinetic energy releases are larger than expected statistically, in contradistinction to what has been observed for the C−X fragmentations of the halogenobenzene cations. H(D) loss from C6H6 + (C6D6 +) occurs via a conical intersection connecting the 2A2 and 2A1 electronic states. Two models are proposed to account for the experimental data:  (i) a modified orbiting transition state theory (OTST) approach incorporating electronic nonadiabaticity; (ii) an electronically nonadiabatic version of the statistical adiabatic channel model (SACM) of Quack and Troe. The latter approach is found to be preferable. It leads to the conclusion that the larger the energy stored in the transitional modes, which partly convert to the relative interfragment motion, the shorter the value of the reaction coordinate at which the adiabatic channels cross, and the larger the probability of undergoing the 2A2 → 2A1 transition required for hydrogen loss.