Nonempirical models of complexes with linear H-bonds

Ab initio Hartree-Fock-Roothaan calculations of the potential energy surfac es or H2O...HX (X = F, Cl) complexes were performed to construct an optimal (in the sense of both accuracy and simplicity) model for calculating the l ow-frequency vibrational band shift of an arbitrary monomer Y caused by the formation of a weakly bound H2O...Y complex under atmospheric conditions. The model only uses the parameters of the one-dimensional potential functio n of anharmonic oscillator Y in the field of the H2O molecule. This approac h is justified by adiabatic separation of vibrational variables of the fast and slow subsystems in H-bonded complexes.