Ab initio studies of the structures and vibrational spectra of the hydrogen halide and lithium halide homo- and heterodimers and some mixed hydrogen halide/lithium halide heterodimers

The dimers of the hydrogen halides and the lithium halides are bound through hydrogen-bonded and lithium-bonded interactions, respectively, and there are many features that the two types of interaction have in common, as well as several fundamental differences. The mixed halide dimers HX·LiY (X, Y=F, Cl, Br) could, in principle, be bound in either of the two ways, and it is one of the aims of this paper to determine which factors are responsible for the particular mode of binding for any given combination of hydrogen halide and lithium halide. The structures, interaction energies, vibrational spectra and bonding characteristics are examined by ab initio molecular orbital theory. In addition, the partitioning of the interaction energies into their various components (electrostatic, induction, dispersion and Pauli exchange) is carried out, and the essential aspects determining the distribution of the particular components in each case are identified.