C-C AND C-H BOND SPLITS OF LASER-EXCITED AROMATIC-MOLECULES .1. SPECIFIC AND THERMALLY AVERAGED RATE CONSTANTS

Toluene, m-, o-, and p-xylene, mesitylene, ethyl-, isopropyl-, and tert-butylbenzene were irradiated by nanosecond laser flashes at 193 nm. After fast internal conversion to the electronic ground state, the molecules dissociate by C-C or C-H bond splits. The products of the fragmentation were identified by comparison with the UV spectra of products from the photolysis of the corresponding α-bromoalkylbenzenes. Toluene, the xylenes, and mesitylene predominantly dissociate by C-H bond split in the methyl groups, the α-methyl-substituted toluenes dissociate by C-C bond split into methyl + substituted benzyl radicals. Specific rate constants k(E,J) for the dissociations were determined in low-pressure experiments with an extrapolation to zero pressure. Statistical adiabatic channel (SACM) calculations of k(E,J) are fitted to the experiments and used to calculate the corresponding high-pressure rate constants for thermal dissociation and recombination. © 1990 American Chemical Society.