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

We report a new three-dimensional potential energy surface for the He–CS2 complex including the Q3 normal mode for the υ3 antisymmetric stretching vibration of the CS2 molecule. The potential energies were calculated at the coupled-cluster singles and doubles with noniterative inclusion of connected triples level with augmented correlation-consistent quadruple-zeta basis set plus midpoint bond functions. Two vibrationally averaged potentials with CS2 at both the ground (υ = 0) and the first excited (υ = 1) υ3 vibrational states were generated from the integration of the three-dimensional potential over the Q3 coordinate. Both potentials have a T-shaped global minimum and two equivalent linear local minima. The radial discrete variable representation/angular finite basis representation method and the Lanczos algorithm were applied to calculate the rovibrational energy levels. Our calculated results show that the two potentials support eight vibrational bound states. The calculated band origin shift of the complex (0.1759 cm−1) agrees very well with the observed one (0.1709 cm−1). The predicted infrared spectra and spectroscopic constants based on the two averaged potentials are in excellent agreement with the available experimental values.