Unimolecular dynamics of hydrogen atom release from excited cycloheptatriene, toluene, and p-xylene

Hydrogen atoms from the photodissociation of cycloheptatriene, toluene, and p-xylene were monitored by laser induced fluorescence using a tunable laser at 121.6 nm. The rates of formation of hydrogen atoms agree with a literature value for the rates of formation of benzyl radicals, the other fragments. The kinetic energy distributions of the nascent hydrogen atoms were derived from the Doppler broadening of the excitation spectra. The average fraction of the available energy released as translational energy was 11%–13%. The data are consistent with a statistical model in which at the instant of dissociation the remaining internal energy is distributed over only a fraction of the vibrational modes.