15min:
HIGHLY PREDISSOCIATIVE LEVELS OF THE CH3S A 2A1 STATE DETERMINED WITH DEGENERATE FOUR-WAVE MIXING.

YUAN-PERN LEE AND YOSHIYUKI MATSUDA, Department of Chemistry, National Tsing Hua University, Hsinchu, Taiwan 30013.

We have determined highly predissociative levels of the A 2A1 state of CH3S in a supersonic jet with degenerate four-wave mixing (DFWM) technique. The highest level observed lies 4265 cm-1 above the zero-point-energy level, much greater than corresponding values of 2979 cm-1 observed by fluorescence depletion spectroscopy and 1490 cm-1 by laser-induced fluorescence. Unlike in fluorescence spectra, relative intensities of lines in DFWM spectra closely reflect their Franck-Condon factors; vibronic assignments are thus more straightforward. A new progression involving excitation of the CH3 stretching mode is identified, and several lines in the range 1290-1410 cm-1 above the origin may be assigned to the CH3 deformation ( nu 5) and the first overtone of CH3 rocking (2 nu 6) modes. Observed vibrational wave numbers are consistent with theoretical predictions.