A computational study of linear HHeF⋯Rg complexes (Rg=He, Ne, Ar, Kr)

The shift in the harmonic vibrational frequency of the He-H stretch of FHeH on formation of the linear FHeH⋯Rg complexes (Rg=He, Ne, Ar, Kr) was determined by ab initio computations. These shifts are in agreement with predictions from a model based on perturbation theory and involving the first and second derivative of the interaction energy with respect to displacement of the He-H bond length from its equilibrium value in the monomer. In the FHeH⋯Rg dimers blue shifts were obtained for all four complexes. The blue shifts are rationalized by considering the balance between the interaction energy derivatives obtained from the perturbative model. The bond length changes on complexation are also well predicted by the model.