DETERMINATION OF AN IMPROVED INTERMOLECULAR GLOBAL POTENTIAL-ENERGY SURFACE FOR AR-H2O FROM VIBRATION-ROTATION-TUNNELING SPECTROSCOPY

A new highly accurate and detailed intermolecular potential surface Ar-H2O is derived by a direct nonlinear least squares fit to 37 far infrared, infrared, and microwave spectroscopic measurements. The new potential (denoted AW2) gives a much better description of the strong radial dependence of the anisotropic forces and of the binding energy than its predecessor, the AW1 surface [Cohen and Saykally, J. Phys. Chem. 94, 7991 (1990)]. The global minimum on the AW2 potential (D(e) = 142.98 cm-1) occurs at the position R = 3.636 angstrom, theta = 74.3, and phi = 0-degrees. At these coordinates the argon is located in the monomer plane between the perpendicular to the C2 axis (theta = 90-degrees) and the hydrogen bonded geometry (theta = 55-degrees). This orientation of the minimum is opposite of that found in recent ab initio calculations of Bulski et al. [J. Chem. Phys. 94, 8097 (1991)] and Chalisinski et al. [J. Chem. Phys. 94, 2807 (1991)]. Both sets of authors find a minimum at an antihydrogen bonded geometry corresponding to an orientation Ar-OH (theta = 125-degrees).