Laser-induced fluorescence of jet-cooled chlorotoluene molecules

Abstract

The laser-induced fluorescence spectra of jet-cooled o-, m- and p-chlorotioluene molecules in the S 1 state are reported. The fluorescence excitation spectra of these molecules exhibit a variety of vibrational modes in the S 1 state. The spectra of m- and p-chlorotoluene show low-frequency bands up to 200 cm −1 above the S 1 origin, which are assigned to internal rotational modes of the methyl group. From 300 cm −1 up to approximately 1500 cm −1, sharp vibrational bands appear; these are assigned by measuring the dispersed fluorescence spectra on excitation of each vibrational band. The vibrational energies of the CCl symmetric stretching mode for o-, m- and p-chlorotoluene molecules are 341 cm −1, 378 cm −1 and 360 cm −1 in the S 1 state respectively. Other prominent normal modes are also assigned.