A new four-dimensional ab initio potential energy surface and rovibrational spectra for the C2H2-Ar complex

We report a new four-dimensional potential energy surface for the C2H2-Ar complex involving the and normal modes for the symmetric stretching and asymmetric stretching vibration of the C2H2 molecule. The potential was constructed at the coupled-cluster singles and doubles with noniterative inclusion of connected triples [CCSD(T)]-F12 level with augmented correlation-consistent polarized-valence triple-zeta (aug-cc-pVTZ) basis set supplemented with midpoint bond functions (3s3p2d1f1g). Two vibrationally averaged potentials with C2H2 at the vibrational ground and excited states were obtained by the integration of the potential over the and coordinates. It was found that each averaged potential has two equivalent T-shaped global minima, two equivalent local minima as well as three saddle points among them. The global minima are located at = 3.97 angstrom, = 61.4 degrees/118.6 degrees with a well depth of 125.47 cm(-1). The rovibrational energy levels and bound states were calculated adopting radial discrete variable representation (DVR)/angular finite basis representation (FBR) and the Lanczos algorithm. The calculated band origin for C2H2-Ar is red-shift by -0.9937cm(-1) in the region of C2H2, which reproduces the observed value of -1.0749cm(-1) successfully. Furthermore, the calculated microwave and infrared transition frequencies are in well good agreement with the experiment data. [GRAPHICS] .