Vibration-rotation spectra of HCl in rare-gas liquid mixtures:: Molecular dynamics simulations of Q-branch absorption

New experimental results are presented on the fundamental IR band shape of HCl dissolved in neat liquid Ar and Ar doped with Kr and Xe. A strong enhancement of the absorption in the range of a central Q-branch is observed in the spectra of doped solutions. Semiclassical molecular dynamics simulations of the spectral band profile are carried out using (12-6) Lennard-Jones site-site interaction potentials. The parameters of these model potentials were deduced by fitting the available anisotropic interaction surfaces, accurately describing the structure of binary rare-gas-HCl van der Waals complexes. Simulations realistically reproduce the observed triplet band structure and its evolution with changing thermodynamic conditions. The analysis of the influence of anisotropic interactions on the orientational dynamics of solutes and orientation-dependent radial distribution functions reveals the mechanisms that contribute to appearance of the Q-branches. It is shown that long-living solute-solvent spatial correlations present in liquid solutions retain to some extent the properties of van der Waals complexes. (C) 2002 American Institute of Physics.