The <i>S</i>1–<i>S</i>(1<i>B</i>2–1<i>A</i>1) transition of jet-cooled toluene: Excitation and dispersed fluorescence spectra, fluorescence lifetimes, and intramolecular vibrational energy redistribution

Abstract

The fluorescence excitation spectrum of the S1–S0(1B2–1A1) transition in jet-cooled toluene has been measured up to 2000 cm−1 above the origin band. Dispersed fluorescence spectra of the major features have been recorded and used to assign the levels observed in excitation. Collisional energy transfer experiments have been used to confirm assignments for some of the lower lying S1 fundamentals that were not accessible via direct optical pumping. The number of known S1 fundamentals has been extended to 13. The dispersed fluorescence spectra reveal the onset of intramolecular vibrational energy redistribution (IVR) at low S1 vibrational energies. Fluorescence lifetimes of all of the major bands observed in the excitation spectrum have been measured. The lifetimes decrease from 86 ns for 00 to 48 ns at an S1 vibrational energy of 1900 cm−1. To alleviate the confusion that exists over the mode numbering in toluene a new scheme is proposed which obviates this problem. This system is similar to that used for other substituted aromatics and should rationalize future work.