Variationally exact rovibrational spectra of nonrigid triatomics: The HeHF van der Waals molecule

A variationally exact method of obtaining the rovibrational levels of triatomic potentials is presented. This LC-RAMP method derives from the close-coupling approach in body-fixed coordinates, but uses optimized Morse oscillator functions to give radial basis sets for both the diatomic and complex stretching coordinates. The method is suited to the nuclear dynamics of nonrigid molecules and atom–diatom van der Waals complexes. A recent full interaction surface for HeHF is fitted and used for dynamical calculations. The binding energy of the complex increases slowly with HF vibrational excitation. Correlation between the HF and complex vibrational modes is found to be negligible.