New He-CO interaction energy surface with vibrational coordinate dependence .1. Ab initio potential and infrared spectrum

The intermolecular potential energy surface of the He-CO complex including the CO bond length dependence has been calculated using symmetry-adapted perturbation theory (SAPT). The potential has a minimum of epsilon(m) = -23.734 cm(-1) with R-m = 6.53 bohr at a skew geometry (theta(m) = 48.4 degrees) if the molecular bond length is fixed at the equilibrium value of 2.132 bohr. We have applied the potential in the calculation of bound state levels and the infrared spectrum for the He-3-CO and He-4-CO complexes. The computed ab initio transition frequencies are found to agree within 0.1 cm(-1) with experiment. In paper II [J. P. Reid, H. M. Quiney, and C. J. S. M. Simpson, J. Chem. Phys. 107, 9929 (1997)], the potential surface is used to calculate vibrational relaxation cross sections and rate constants. (C) 1997 American Institute of Physics. [S0021-9606(97)03146-2].