Fermi-resonances, potential energy function, and cluster-like spectra of the ground electronic state of CS 2

Abstract

The rotationally resolved stimulated emission pumping spectra of the ground electronic state X̌ 1Σ + g of CS 2 from 3290 to 16 370 cm −1 have been recorded by using a three-level polarization spectroscopy technique. The vibrational analysis was carried out by using a normal coordinate model. In addition to the 〈 ν 1−1, ν 2 ℓ+2, ν 3|H| ν 1, ν 2 ℓ, ν 3〉 Fermi-resonance, the 〈 ν 1−3, ν 2 ℓ+4, ν 3|H| ν 1, ν 2 ℓ, ν 3〉 type of anharmonic resonance was found. The parameters of the potential energy function were given in both the normal mode and the internal coordinate representations. As the energy was increased to above 13 400 cm −1, the spectra gradually developed cluster-like features. Such cluster-like features were interpreted as anharmonic resonance polyads. The dependence of the onset of the cluster-like features on the energy and on the initial conditions was studied by using a classical trajectory calculation.