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A procedure for diabatization of quantum-chemical data is proposed that allows one to surmount the problem of -shaped peaks of nonadiabatic matrix elements by passing to a hybrid diabatic representation of a system of coupled channel equations of nuclear dynamics with the use of model nonadiabatic matrix elements that approach initially specified matrix elements. Results of the application of this method within the framework of the Landau-Zener model are presented for the example of the CaH collision system. [ABSTRACT FROM AUTHOR]

Radiative transitions occurring at atomic collisions are considered. Attention is focused on the transitions that are either impossible in individual atoms or ions or forbidden by the selection rules. The excitation of continuous-spectrum electron states is considered for the first time by an example of photodetachment at collisions of negative ions with neutral atoms. [ABSTRACT FROM AUTHOR]

We have studied exchange processes in contact complexes of triplet eosin molecules with oxygen molecules in the triplet (Σ) and singlet (Δ) states in thin polyvinylbutyral films in the presence of gold nanoparticles. Upon resonant excitation of surface plasmons in gold nanoparticles into the absorption band of eosin molecules-singlet oxygen sensitizers-we have obtained an increase in the intensity of the delayed fluorescence and an increase in the lifetime of the dye with simultaneous quenching of the luminescence of singlet oxygen. The kinetics of the delayed fluorescence of the dye as a result of singlet-triplet annihilation of triplet eosin molecules with singlet oxygen molecules has been investigated. To compare theoretical and experimental data, we have numerically simulated energy transfer processes. Rate constants of energy transfer and of singlet-triplet annihilation, as well as quenching constants of triplet states of the dye by molecular oxygen, have been calculated. Luminescence quantum yield Δ of polyvinylbutyral has been estimated. We have analyzed quantum-chemically electronic mechanisms of singlet-triplet annihilation of oxygen and eosin. [ABSTRACT FROM AUTHOR]

A van der Waals complex that consists of a deuterium molecule in the ortho state and a carbon monoxide molecule, CO- ortho-D2, was studied in the frequency range 85–130 GHz with the help of an intracavity orotron-based spectrometer. Nine new lines, which correspond to rotational transitions and belong to the R and Q branches, were measured and identified. The positions of the rotational energy levels of CO- ortho-D2 were refined by comparative analysis of the transition frequencies measured in this work and previously reported microwave and infrared data. [ABSTRACT FROM AUTHOR]

Van der Waals complexes consisting of helium atoms and carbon monoxide molecules, He-12C16O, He-13C16O, He-12C18O, and He-13C18O are studied in the frequency range 110–140 GHz on an intracavity orotron-based spectrometer. Ten new lines, which correspond to rotational transitions and transitions to the bending vibration of the complex, are detected and identified as lines belonging to the R and P branches. The positions of the energy levels of isotopologue of the He-CO complex are refined by joint analysis of both the transition frequencies measured in this study and previously published microwave and infrared data. Isotopic dependences of the positions of the He-CO energy levels are obtained. These results can serve as the starting point for studying small helium clusters with embedded CO molecules. [ABSTRACT FROM AUTHOR]

The three-dimensional vibrational problem for the isolated van der Waals complex formed by the Li+ cation with the N2 molecule is solved by the variational method. The potential energy and dipole moment surfaces are calculated using different basis sets of atomic functions and different approaches for taking electron correlation into account. The anharmonic effects caused by the interaction of vibrational degrees of freedom of the complex are consistently considered for the first time. The energy levels of three-dimensional vibrational states are determined. The frequency shift of the N2 molecule vibration upon complexation and the fundamental transition intensity for this vibration in the complex are calculated. The frequencies and intensities for a number of spectral transitions between the states associated with excitation of low-frequency modes are determined. The average values of geometrical parameters and their variances are calculated for the ground state and excited vibrational states of the complex. [ABSTRACT FROM AUTHOR]

A theory of radiative–collisional transitions between the ground and metastable 1S states of a colliding atom is proposed. The theory uses the uniform quasi-classical approximation generalized to the case of spherically asymmetric interactions. The theory takes into account the angular momentum of an emitted (absorbed) photon and allows one to calculate the total and differential scattering cross sections in a wide range of radiation frequencies including both wings and the center of the line of a forbidden atomic transition. The range of admissible collision energies and intensities of an external radiation field is restricted by the use of the adiabatic approximation, as well as the approximation of a weak coupling between the ground and excited states of a quasi-molecule, the potentials of which are assumed to be monotonically repulsive. © 2005 Pleiades Publishing, Inc. [ABSTRACT FROM AUTHOR]

A new semiempirical approach is proposed for describing the regularities of the shift of the absorption bands in the IR spectra of ultimately ordered van der Waals complexes of 1 : 1 composition upon the gas–solution phase transition. This approach is based on the analysis of the specific features revealed in the combined effect exerted by nonlinear (complex formation) and linear (solvation) dipole–dipole interactions on the change in the electrical and electro-optical parameters of the absorbing molecule in the structure of solvated complexes. It is shown that the concepts developed enable correct quantitative interpretation of a large amount of available experimental data for complexes of an HCl molecule with molecules of acetone and acetonitrile in a number of nonpolar solvents. © 2005 Pleiades Publishing, Inc. [ABSTRACT FROM AUTHOR]

We suggest a semiempirical approach to describing the influence of local nonlinear dipole–dipole interactions on the formation of van der Waals complexes of 1 : 1 composition in the gas phase. Based on this approach, we quantitatively interpret the experimental data on the patterns of the shift in the electronic (complexes of a 3-aminophthalimide molecule with water and methanol molecules) and vibrational (complexes of a HCl molecule with acetone and acetonitrile molecules) absorption spectra attributable to the processes of complex formation. We confirm the conclusion that a nonlinear dipole–dipole interaction should be considered as one of the most important physical mechanisms that result in the association of molecules both in the gas phase and, under certain conditions, in the condensed state. © 2003 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]