Rydberg–Klein–Rees inversion of high resolution van der Waals infrared spectra: An intermolecular potential energy surface for Ar+HF (v=1)

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Abstract
A method is described for extraction of two‐dimensional (angular and radial) potential energy surfaces for triatomic rare gas–hydrogen halide van der Waals complexes. The approach relies on extensive J rotational term values obtained by high resolution infrared laser jet spectroscopy for a family of bending vibrational states to deduce the radial and angular dependence of the intermolecular potential. First, effective 1D radial potentials for a series of bending states are obtained by rotational RKR analysis of experimentally observed rotational progressions. These 1D potentials, which represent vibrational averages over different bending wave functions, are then inverted to determine the radially dependent coefficients of a Legendre expansion to the full surface, i.e., ∑lVl(R)Pl (cos θ). This relies on adiabatic angular motion with respect to radial degrees of freedom, the validity of which is discussed. This approach is tested with experimental data from the (100 0) (fundamental), (120 0) (HF parallel bend), and (111 0) (HF perpendicular bend) of Ar+HF (v=1), excited up to J≤25. The accuracy of the resulting surface is verified by exact quantum bound state calculations which quantitatively reproduce the rovibrational input data, as well as predict the spectroscopic properties of five other vibrational states observed in the Ar+HF (v=1) system but not used in the fitting procedure.