Laser-induced fluorescence and fluorescence depletion spectroscopy of SCCS−

Abstract

In a discharged supersonic jet of carbon disulfide, a band system of a new species is observed by laser-induced fluorescence (LIF) spectroscopy. Rotationally resolved spectra show that the observed electronic transition is Π23/2−Π23/2. Since both sulfur and carbon atoms have even numbers of electrons, it is concluded that the spectral carrier is an ionic species. Furthermore, the spectral carrier is confirmed to have two equivalent carbon atoms from the LIF spectra of the C13-substituted species. With a help of ab initio calculations, the carrier is identified as the linear negative ion SCCS−, where the observed electronic transition is considered to be à 2Πg–X̃ 2Πu. A mass spectrometric measurement also gives evidence that SCCS− is produced in the discharged jet. The vibrational structure for the upper electronic state is determined by both LIF and fluorescence depletion spectroscopy. A dispersed fluorescence spectrum is also observed to determine the vibrational structure of the lower electronic state. Frequencies of the ν1 (C–C stretching) and ν2 (C–S symmetric stretching) vibrational modes are determined for both the electronic states, which are in good agreement with the theoretically calculated values. Fluorescence decay profiles are obtained for many vibronic levels, and the excited-state dynamics is discussed based on the determined fluorescence lifetimes and results of ab initio calculations.