Fermi resonance switching in KrHRg and XeHRg (Rg = Ne, Ar, Kr, and Xe).

Matrix isolation experiments have been successfully employed to extensively study the infrared spectrum of several proton-bound rare gas complexes. Most of these studies have focused on the spectral signature for the H stretch (ν) and its combination bands with the intermolecular stretch coordinate (ν). However, little attention has been paid to the Fermi resonance interaction between the H stretch (ν) and H bend overtone (2ν) in the asymmetric proton-bound rare gas dimers, RgHRg'. In this work, we have investigated this interaction on KrHRg and XeHRg with Rg = (Ne, Ar, Kr, and Xe). A multilevel potential energy surface (PES) was used to simulate the vibrational structure of these complexes. This PES is a dual-level comprising of second-order Møller-Plesset perturbation theory and coupled-cluster singles doubles with perturbative triples [CCSD(T)] levels of ab initio theories. We found that when both the combination bands (nν + ν) and bend overtone 2ν compete to borrow intensity from the ν band, the latter wins over the former, which then results in the suppression of the nν + ν bands. The current simulations offer new assignments for the ArHXe and KrHXe spectra. Complete basis set (CBS) binding energies for these complexes were also calculated at the CCSD(T)/CBS level.