New aspects of the lsquo;lsquo;channel threersquo;rsquo; problem in benzene, as revealed by multiphoton ionization photoelectron spectroscopy

摘要

Combining a photoelectron spectroscopic technique with a (1+1) resonant ionization method, we have investigated intramolecular decay processes of benzene in itsS1state under collisionhyphen;free conditions. Photoelectron spectra were obtained by selective excitation of benzene with a pulsed UV laser at several single vibronic levels of theS1state up to an internal energy (Dgr;E) of 5000 cmminus;1. These spectra strongly suggest that the excitation of benzene at the vibronic bands above the onset of the lsquo;lsquo;channel threersquo;rsquo; is followed by intramolecular vibrational redistribution within theS1state. It is concluded that there are no decay channels faster than this redistribution process up to Dgr;E=5000 cmminus;1at the first decay stage. The results of the integrated multiphoton ionization intensity distribution over the vibronic bands, as well as the internalhyphen;energy dependent spectral changes observed in the photoelectron spectra, also strongly suggest that the channel three is initiated by the redistributed vibrational modes, which lead to a fast internal conversion leads to the ground electronic state.