VIBRATIONAL DEPENDENCE OF THE ANISOTROPIC INTERMOLECULAR POTENTIAL OF AR-HF

A new intermolecular potential for Ar-HF is obtained by fitting to results from high-resolution microwave, far-infrared, and infrared spectroscopy. The new potential, designated H6(4,3,2), is a function of the diatom mass-reduced vibrational quantum number eta = (upsilon + 1/2)/(mu(HX))1/2 as well as the intermolecular distance R and angle theta, and has 22 adjustable parameters. It reproduces all the available spectroscopic data for levels of Ar-HF correlating with HF, upsilon = 0, 1, and 2, and DF, upsilon = 0 and 1. The H6(4,3,2) potential is qualitatively similar to previous potentials, with a linear Ar-H-F equilibrium geometry and a secondary minimum at the linear Ar-F-H geometry. Compared to the potential of Nesbitt et al. [J. Chem. Phys. 90, 4855 (1989)], obtained from spectra of Ar-HF (upsilon = 1), the H6(4,3,2) potential is rather deeper near the equilibrium geometry (Ar-H-F), but shallower around the secondary minimum (Ar-F-H). The absolute well depth increases by 19 cm-1 between HF upsilon = 0 and upsilon = 1. The vibrationally averaged induction energy is calculated to be substantially (8.1 cm-1) greater for upsilon = 1 than for upsilon = 0, and is responsible for most of the observed red shift in the complex. Predictions of additional spectroscopic properties that would test the new potential are given, including far-infrared and overtone spectra of Ar-DF and dipole moments of excited states of Ar-HF and Ar-DF.