PHOTON-INDUCED UNIMOLECULAR DECAY OF THE BENZYL RADICAL - 1ST DIRECT IDENTIFICATION OF THE REACTION PATHWAY TO C7H6

The thermal unimolecular decay of the benzyl radical has been investig ated extensively by several groups. However, the reaction products cou ld not be determined unambiguously. In this work the unimolecular bond fission of the benzyl radical is studied in a molecular beam experime nt. The precursor molecules toluene and cycloheptatriene are expanded in a molecular beam and photodissociated with two photons at 248 or 19 3 nm, yielding in each case hot benzyl radicals. Since the internal en ergies lie above the dissociation limit, the benzyl radicals decay in a subsequent step. The reaction products are detected in a time-resolv ed manner with a quadrupole mass spectrometer on the molecular beam ax is at low electron energies. The measured time-of-flight spectra provi de information on the translational energy distribution of the product s. In each case it is found that the hot benzyl radicals C7H7 fragment under hydrogen loss to C7H6.