Excitation and dispersed fluorescence spectra of the 1B2(V)-1Σg+(X̄) transition of jet-cooled CS2

Abstract

Abstract The fluorescence excitation and dispersed fluorescence spectra of the transition 1B2(V)-1Σg+(X) of jet-cooled CS2 have been measured. Vibrational analysis of the spectra has been carried out with the aid of ab initio calculations of the adiabatic potential in the excited state and of a Fermi resonance calculation of the ground-state vibrational levels. The calculated potential indicates a drastically bent structure in the excited state (θSCS = 131°±5°, RCS = 1.645±0.01 A) which explains the observed fluorescence spectra having extremely long progressions of the overtone of bending mode 2ν″2. The electronic origin of the transition has been found at 30530 cm−1 and the irregularly spaced vibronic levels in the excited state have been interpreted by a model potential V(θ) = − k2θ2 + k4θ4 along the bending coordinate θ with a central barrier height of 2000–2750 cm−1. The anomalous Franck-Condon intensity distribution of the fluorescence spectrum is also discussed in terms of the anharmonic potential and the nuclear coordinate dependence of the transition moment.