Laser-induced fluorescence spectroscopy of the jet-cooled methylthio radical

Abstract

Laser-induced fluorescence excitation and wavelength-resolved emission spectra have been recorded for the methylthio (CH3S) radical in a supersonic jet environment. Twenty one vibronic bands have been obtained in excitation in the 360-387 nm region with about 0.2 cm-1 resolution and assigned to the A 2A1 - X 2E3/2 and A 2A1 - X 2E1/2 electronic transitions. Fluorescence from five vibronic bands (000, 301, 302, 312 and 201310) has been individually dispersed by a 0.6 m monochromator with a resolution of 0.3 nm. To the best of our knowledge, the wavelength-resolved emission spectra of CH3S for the 312 and 201310 bands are being reported here for the first time and these provide new vibrational intervals hitherto unobserved. Fundamental vibrational frequencies have been determined for the nu2 (umbrella) and nu3 (C-S stretch) modes of CH3S for both the excited A 2A1 state and the ground X 2E state: nu'2=1096 cm-1, nu'3=402 cm-1, nu2=1328 cm-1 and nu3=742 cm-1. In addition, the nu6 (rocking) mode vibrational frequency has been obtained for the A 2A1 state, i.e. nu'6=628 cm-1. Vibrational and anharmonic parameters have been determined by a least-squares fit of the progressions involving the symmetric nu3 vibration in the A 2A1 - X 2E3/2 excitation spectra and involving both the nu2 and nu3 progressions in the dispersed fluorescence spectra.