RC12		15 min11:40

YUAN-PERN LEE, MIN-YI SHEN AND WEN-CHING HUNG, Department of Chemistry, National Tsing Hua University, Hsinchu, TAIWAN 30043.

The ethylthio (C₂H₅S) radical was formed by 248-nm laser photolysis of diethyl disulfide (C₂H₅SSC₂H₅) or ethyl mercaptan (C₂H₅SH) in a free jet expansion. The B - X fluorescence excitation spectrum was recorded in the wavelength region 398 - 440 nm. Preliminary data show that the origin lies at 23519.6 cm^-1 with a main progression of C-S stretching (420.5 cm^-1). Other vibrational modes at 256.0, 861.0, 1054.6, and 1203.3 cm^-1 were also observed for the B state. Detection of hot bands in the excitation spectrum enables assignments of three low-lying modes of the X state: 296.2, 479.9, and 672.8 cm^-1. Dispersed fluorescence spectra in the spectral region 410 - 520 nm revealed a main progression of C-S stretching (673 cm^-1 with additional vibrational modes of the X state near 308, 475, 882, 1076, and 1257 cm^-1. Observed vibrational wavenumbers of both B and X states agree with theoretical calculations by the B3LYP/cc-PVDZ+f method (for the X state) and the MP2/DZP method (for both states).