Vibrational Spectroscopy and Potential Energy Surface Analysis of the X˜ And B˜ States of Thiophosgene

Abstract

Nearly 1,000 B˜(1A 1) → X˜(1A 1) vibronic transitions of SCCl2, originating from eight B˜(1A1) state vibrational levels, have been measured by dispersed fluorescence spectroscopy. More than 370 of these vibrational fundamentals, overtones, and combination bands were assigned and fit with a simple spectroscopic Hamiltonian. Observed transitions are highly Franck-Condon active in the CS stretching (nu1) and out-of-plane bending (nu4) modes, and extend in energy beyond the lowest molecular dissociation threshold. A full six-dimensional potential energy surface transformed to a normal coordinate representation has been fit to the experimental X˜(1 A1) levels up to 8,000 cm-1. A six-dimensional multi-reference PES has also been fit, to a series of CASSCF ab initio calculations modeling the B˜(1 A1) state. Wavefunctions for both the X˜ (1A1) and B˜ (1A1) states were calculated in harmonic oscillator bases using the same normal coordinate representations. Along with an electronic transition dipole surface generated from the CASSCF points, the wavefunctions were used to calculate B˜( 1A1) → X˜( 1A1) vibronic transition intensities. In addition, SCCl2 is an excellent system for exploring vibrational dynamics. One scheme for measuring vibrational dephasing in SCCl2 is presented. The multi-photon scheme was developed from spectroscopic investigations of the molecule's fluorescence lifetimes, (pre-) dissociation thresholds, and electronic state multi-photon up-pumping tendencies.