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The substructure of the infrared spectrum for acetone-HF hydrogen-bonded complex has been reconstructed for the first time using ab initio calculations at the self-consistent-field approximation. Vibrational calculations of the νFH and νF···O transitions taking into account the mechanical anharmonicity effects have been made using a variational method. The main shoulders of the infrared spectrum are interpreted in terms of combination transitions and hot combination transitions. [ABSTRACT FROM AUTHOR]

Ab initio self-consistent field (SCF) and MP2 calculations have been performed in order to investigate the structure, energetics, and spectroscopic properties of H2O: (HF)2. Two conformations of the 1:2 complex are energetically possible. On the one hand is a cyclic complex belonging to the C1 point group and which corresponds to the absolute minimum, and on the other hand is a bifurcated complex with C2v symmetry. In this latter complex the two hydrogen bonds are equivalent whereas in the former there are two strong H-bonds and a weaker one. The energy difference between these two conformers is ∼3 kcal mol-1. From the spectroscopical point of view the bifurcated complex is characterized by νHF frequency shifts smaller than that calculated for the dimer, in the case of the cyclic complex the two different νHF red shifts closely related to the H2O–HF and (HF)2 calculated shifts, respectively, and correspond to those experimentally observed. The cooperative effects on interaction energies and spectroscopic properties have been estimated and analyzed on the basis of the projected induced dipole moment. It is shown that the cyclic complex is favored with respect to both H2O–HF and (HF)2 precursors while the formation of the bifurcated one remains more problematic. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]