A new four-dimensional ab initio potential energy surface and predicted infrared spectra for the He–CS₂ complex

Abstract

We present a new four-dimensional ab initio potential energy surface for He–CS₂ that is constructed at the coupled cluster and doubles with noniterative inclusion of connected triple [CCSD(T)] level with augmented correlation-consistent quadruplet-zeta (aug-cc-pVQZ) basis set plus midpoint bond functions. The $Q_{1}$ and $Q_{3}$ normal modes for the $\nu_{1}$ symmetric stretching vibration and $\nu_{3}$ antisymmetric stretching vibration of CS₂ are involved in the construction of the He–CS₂ potential. Two vibrationally averaged potentials with CS₂ at the vibrational ground and the $\nu_{1} \text{ + }\nu_{3}$ excited states are generated from the integration of the four-dimensional potential over the $Q_{1}$ and $Q_{3}$ coordinates. Each potential is found to have a T-shaped global minimum. The radial discrete variable representation/angular finite basis representation method is employed to calculate the rovibrational states without separating the inter- and intramolecular vibrations. The calculated shift of band origin (0.2270 cm⁻¹) agrees well with the experimental value (0.2278 cm⁻¹). The frequencies and line intensities of the rovibrational transitions in the $\nu_{1} \text{ + }\nu_{3}$ region of CS₂ for the vdW vibrational ground state are also in good agreement with the observed infrared spectra.