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.