Structure and vibrational properties of water hydrogen halide complexes

A series of self-consistent field (SCF) calculations has been carried out on the 1:1 hydrogen bonded complexes of water and hydrogen halide (HF,HCl,HBr,HI) using core pseudopotentials and PS-31G** basis sets. The geometry optimization confirm the Cs structure predicted by the Legon–Millen rules. Electron density difference (complex superposition of isolated molecules) emphasize the role of polarization effects in this type of hydrogen bond. Finally, the HX frequency shifts with respect to monomeric species, the intensity ratios of the corresponding IR lines and the intermolecular stretching frequencies have been calculated by a variational method which takes into account both coupling and anharmonicity effects. An overall agreement with experimental data is obtained for these spectroscopic properties.