Stretching force constants as descriptors of energy and geometry of F···HF hydrogen bonds.

In this work applicability of proton donor group stretching vibration force constants k and intermolecular stretching force constants k for evaluations of hydrogen bond strength and geometry are discussed. For a set of 30 complexes with F···HF hydrogen bonds in a wide range 0.5-48 kcal/mol by means of quantum chemical calculations equilibrium geometries, complexation energies, vibrational frequencies and corresponding force constants were calculated (MP2/aug-cc-pVTZ).

Lone pairs mapping by Laplacian of He NMR chemical shift.

Results of approbation of a new quantum mechanical approach of lone pairs (LPs) visualization, its optimization and testing on a range of model molecules are presented. The main idea of proposed methodology is using He atom as a probe for investigating electronic shells of species with LPs. As model objects, we consider "classical" examples of hydrogen cyanide, methanimine, ammonia, phosphine, formaldehyde, water, and hydrogen sulfide.

Calculation of vibrational spectroscopic and geometrical characteristics of the [F(HF)] and [F(DF)] complexes using the second-order vibrational perturbation theory and a 6D variational method.

Vibrational spectroscopic and average geometrical parameters of the strong H-bonded complexes [F(HF)] and [F(DF)] are determined for the first time from nine-dimensional (9D) perturbative and 6D variational calculations. The frequencies and intensities for all fundamental and some combination and overtone transitions obtained by the method of second-order vibrational perturbation theory (VPT2) are reported. A two-fold decrease in the H-F (D-F) stretching band frequency and a more than ten-fold increase in the intensity of this band upon complexation are predicted.

Quantum-Mechanical Prediction of the Averaged Structure, Anharmonic Vibrational Frequencies, and Intensities of the HO···trans-HONO Complex and Comparison with the Experiment.

The geometrical parameters, the frequencies, and absolute intensities of vibrational transitions of HO···trans-HONO hydrogen-bonded complex are calculated using the approach earlier tested in calculations of isolated molecules of nitrous acid and complexes of this acid with ammonia. The equilibrium nuclear configuration and potential energy and dipole moment surfaces are calculated by the MP2/aug-cc-pVTZ method with the basis set superposition error taken into account. The fundamental transition frequencies and intensities of the complex are first obtained in the harmonic approximation, and then the energy values, vibrational wave functions, and transition frequencies and intensities are determined from variational solutions of one- to four-dimensional anharmonic equations.

Infrared Studies of the Symmetry Changes of the SiH Molecule in Low-Temperature Matrixes. Fundamental, Combination, and Overtone Transitions.

Infrared spectra of SiH in argon and nitrogen matrixes at low temperature 6.5-20 K in the region of overtone and combination transitions were recorded for the first time. Additionally, the high-resolution spectra were obtained in the fundamental region.