TIME-RESOLVED REMPI DETECTION OF METHYL RADICALS GENERATED IN LASER-INDUCED UNIMOLECULAR REACTIONS

The specific rate constants for the photofragmentation of four substit uted benzene molecules (ethylbenzene, tert-butylbenzene, toluene, benz otrifluoride) following pulsed laser excitation at lambda = 193 nm wer e measured in a molecular beam experiment by monitoring the change of the intensity of the nascent products as a function of time delay betw een excitation and detection laser pulses. In the case of toluene (C6H 5CH3), ethylbenzene (C6H5CH2CH3>, and tert-butylbenzene (C6H5C(CH3)(3) ) a (3+1)REMPI process at lambda = 450.8 nm was used to ionize the CH3 products, which were detected in a time-of-flight mass spectrometer. Following dissociation of benzotrifluoride (C6H5CF3) the trifluormethy l radical CF3 was detected at lambda = 455 nm. The measured specific r ate constants can be modeled satisfactorily by using the SACM (statist ic adiabatic channel model) statistical theory.