Vibronic structure of CCS in the à 3Πi state studied by laser-induced fluorescence spectroscopy

Abstract

Laser-induced fluorescence spectrum of the à 3Πi←X̃ 3Σ− transition of the CCS radical has been studied in a discharged supersonic jet of a mixture gas, carbon disulfide and acetylene diluted in Ar. More than 40 vibronic bands in the 600–925 nm region have been assigned to the transitions from the ground vibronic level of the CCS radical. The progression of the C–C stretching mode was identified for υ1=1–4, and the harmonic frequency of the mode was determined to be 1840.13(1) cm−1. In addition to the perpendicular bands, Σ–Σ parallel-type bands have been observed and assigned to vibronically forbidden transitions, Ã(υ1,0,1)←X̃(0,0,0). Based on the positions of the bands, the harmonic frequency and the Renner parameter of the bending mode in the à 3Πi state were determined to be 399.00(3) cm−1 and −0.234 67(7), respectively. High-level ab initio calculations were performed to compare the results with the experimentally determined vibronic parameters. Since the band at 778 nm has a complicated rotational structure due to the overlap of vibronic levels, a microwave-optical double-resonance method using a Fourier-transform microwave spectrometer and a pulsed laser was applied to obtain a definite rotational assignment.