539.194.01 Ab initio calculations in a harmonic approximation of absorption band absolute intensities in infrared spectra were carried out for 3 hydrocarbons and 14 halogenated hydrocarbons. The calculated data were compared with experimental values of the absolute absorption intensities. It is shown that a Hartree-Fock calculation method overestimates significantly (by an average of 66%) the integrated absolute intensities of the fundamental bands in the region 575-4000 cm -1 . The deviation is reduced to 32% in the case of the MP2 method of accounting for electron correlations. Most of the overestimation occurs for bands corresponding to vibrations involving halogen atoms.

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539.194:541 Frequencies and intensities of fundamental, overtone, and combination absorption bands have been calculated in an anharmonic approximation for substituted benzene and ethene, aldehydes, ketones, and alcohols in the range 400-4000 cm -1 . The calculated values agree well with the experimental data. It is shown that such a calculation allows one to study and predict dependences of the frequencies and intensities of the overtone and combination bands on the substance structure.Statement of the Problem. IR spectroscopy has for a long time used mainly fundamental absorption bands in the range 400-4000 cm -1 . Overtone spectra were utilized rather rarely. Qualitative analyses of substituted benzenes, quantitative determination of alcohols using the intensity of the OH stretching vibration overtone band, and several others can be used as examples [1]. The advantage of using absorption spectra in the range of the fundamental transitions is related to limitations on the overtone region with respect to the experimental technique for recording spectra and theoretical methods for establishing spectra-chemical structure relationships. The experimental technique has recently been developing rather quickly. Not only the intensities of the fundamental absorption bands but also weak overtone and combination absorption bands can be recorded over a broad spectral range, from the far IR to the UV.Knowledge of the rules (spectra-structure correlations) relating the IR spectrum of a compound to its structure is necessary in order to solve the problem of establishing the composition and amount of the compound. Such rules can be found in two ways, empirically and using theoretical calculation methods. The empirical method is quite complicated. For example, the accumulation and systematization of data for fundamental spectra in the range 400-4000 cm -1 took several decades [2]. In instances where a theory relating the spectrum of a compound with its structure has sufficient accuracy, the search for spectra-structure correlations can be significantly accelerated because the mathematical (computer) experiment is cheaper and simpler than the material one. Furthermore, the nature of such rules becomes clear. The current development level of the theory of electromagnetic radiation absorption by matter [3-8] allows rather accurate predictive calculations of spectra in the range of fundamental transitions to be made. The situation is much worse for estimating the probability of overtone transitions.It is worth noting that although the anharmonic problem was discussed in detail in the literature [3][4][5][6][7][8], there have been few attempts to calculate frequencies and intensities of overtone and combination absorption bands. The reason for this is the insufficient development of the computational base and the lack of software. The required technology appeared comparatively recently. The book of Gribov and Pavlyuchko [8] led to an approach based on the variational principle in the form of universal computer programs suitable ...

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Self-action of a spatially annular femtosecond laser beam with spiral phase dislocation in a transparent dielectric with anomalous group velocity dispersion is studied. Based on numerical simulations the analysis of spatiotemporal evolution of intensity distribution in a pulsed optical vortex beam at the wavelength nm in fused silica is carried out. It is predicted the formation of annular light bullets with dynamical localization of intense laser field in thin rings with width of approximately , duration of optical oscillations and intensity higher than W cm−2.