Anharmonic vibrational spectroscopy calculations for novel rare-gas-containing compounds: HXeH, HXeCl, HXeBr, and HXeOH

A first-principles calculation of vibrational spectroscopy of HXeH, HXeCl, HXeBr, and HXeOH molecules is performed by combining ab initio codes with the vibrational self-consistent field (VSCF) method, and with its extension by perturbation theory (CC-VSCF). The MP2/CC-VSCF method is anharmonic, and it is able to reproduce the experimentally observed spectral features of HXeH, HXeCl, HXeBr, and HXeOH. The most intense bands of the HXeY molecules, the Xe-H stretching modes, are found to be highly anharmonic. In general, the other fundamental modes presented anharmonic effects to a lesser extent. New predictions of overtone and combination vibrations are made to help experimental investigations of these molecules. It is shown that vibrational spectroscopy calculations are reliable and useful for analyzing the spectral features of rare-gas-containing molecules. While the results of the MP2/CC-VSCF calculations are in much better agreement with experiments than the corresponding harmonic frequencies, substantial discrepancies remain. These are mostly due to the large electronic correlation effects in these systems, which are not sufficiently well presented at the MP2 level.