Gas phase electronic spectrum of the HSCCS radical by laser-induced fluorescence spectroscopy

In a discharged supersonic jet of a CS2 and C2H2 mixture, a vibronic band system of a new radical species was observed in the energy region 21 800-23 000 cm−1 by laser-induced fluorescence (LIF) spectroscopy. The LIF excitation spectrum shows progressions with 490 and 80 cm−1 separations. The vibronic structure of a dispersed fluorescence (DF) spectrum, obtained by tuning a probe laser to the vibronic origin band, also consists of progressions with 520 and 100 cm−1 separations. A high-resolution laser scan provided a rotationally resolved LIF excitation spectrum for the vibronic origin band, showing the rotational structure of a-type transitions of a near-prolate top. Several chemical tests indicate that the spectral carrier contains sulfur atom(s), one hydrogen atom and more than one carbon atoms. Electronic transition energy, vibrational frequencies, and rotational constants of this species are similar to those of SCCS− [M. Nakajima, Y. Yoneda, Y. Sumiyoshi, T. Nagata, Y. Endo, J. Chem. Phys. 119(2003)7805-7813.], and the spectral carrier was assigned as an isoelectronic radical, bent HSCCS. Ab initio geometrical optimizations supported the spectral carrier to be HSCCS. The observed electronic transition was assigned to be the B∼2A″-X∼2A″ transition, which corresponds to the Π-Π transition in the limit of linear geometry. The observed vibrations in the excitation and DF spectra were assigned as the symmetric CS stretching (ν5) and SCC bending (ν7) modes by comparing the results of theoretical calculations.