Calculated rovibrational energy levels and infrared spectrum of He-C₂H₂

Abstract

Accurate calculations of the energies of all bound rovibrational states, of the energies and lifetimes of some metastable states, and of the resulting rovibrational spectrum are performed for the helium-acetylene Van der Waals complex using an iterative secular equation method. The calculations are carried out both on an empirical potential surface which has a single ‘T shaped’ minimum, and on a potential surface based on ab initio electronic structure calculations which has a single minimum at a linear geometry. The two surfaces differ in the strength of the anisotropy, as well as its sign. A comparison of the spectra generated by the two surfaces allows spectroscopic manifestations of the shape of the potential energy surface to be discerned, results which should help guide analyses of the spectra of similar very weakly bound complexes.