Laser-induced fluorescence of jet-cooled chlorotoluene molecules

The laser-induced fluorescence spectra of jet-cooled o-, m- and p-chlorotoluene 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.