Knowledge Bank

New vibronic band system has been observed in the $21800-23000cm-1$ region by laser-induced fluorescence spectroscopy in a discharged supersonic jet of the $C2H2$ and $CS2$ mixture gas. Several chemical tests indicate that the spectral carrier contains H, C and S atom(s). High-resolution spectra of these vibronic bands show $\Sigma -\Sigma$ type rotational structures. The origin band position and the effective rotational constants of the upper and lower levels have been determined to be $T0=21877.7706(7),Beff\prime =0.04932(1)$ and $Beff\prime \prime =0.05013(2)cm-1$, respectively. Based on the results of ab initio calculations, it is considered that bent HSCCS is the most probable candidate for the spectral carrier.