Knowledge Bank

New electronic transition has been observed in the $18400-19800cm-1$ region by discharging the $CS2$ molecule in a supersonic jet using a laser induced fluorescence technique. Since the vibronic bands completely disappear when the $C2H2$ sample is used, the spectral carrier contains the sulfur atom. Rotationally resolved spectra were obtained by high-resolution laser scans. The band type of all the bands is assigned to $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}\Pi 3/2-2\Pi 3/2$, and the effective rotational constant of the ground electronic state has been determined to be $0.05047(4)cm-1$. We concluded that the ground state of the radical is $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}\Pi i$, and the spectral carrier may be an ionic species because both the carbon and sulfur atoms have even numbers of electrons. Based on the results of ab initio calculations, it is considered that the negative ion, $SCCS-$, is the most probable candidate for the spectral carrier.