T. G. Burova

Quantum-mechanical calculation of the intensity distribution in resonance raman spectra of thiosubstituted derivatives of uracil

A quantum-mechanical calculation of the intensity distribution in the resonance Raman (RR) spectra of 2-thiouracil and 4-thiouracil is carried out for exciting laser radiation at 300, 257, and 248 nm. It is shown that, for satisfactory agreement between the calculated results and the experimental data, it is necessary to take into account in the calculations of the relative intensities of lines the Herzberg-Teller effect and the contribution from excited electronic states adjacent to the resonance state. The general and specific features of the intensity distribution in the RR spectra of uracil and its thiosubstituted derivatives are compared and discussed.

Determination of the tautomeric composition of adenine in the gas phase by vibrational spectroscopy methods: I. Analysis of IR spectra

The tautomeric composition of isolated adenine has been analyzed using computational IR spectroscopy. A comparison with experimental data has demonstrated that, in addition to adenine-N9H, which dominates in the quantitative content, two more tautomers that have the N9H imino and N7H amino forms exist in the isolated state and in the gas phase.

Determination of the tautomeric composition of adenine in the gas phase by vibrational spectroscopy methods: II. Analysis of resonance Raman spectra

The resonance Raman spectra of adenine in the gas phase under excitation with laser radiation at wavelengths of 266, 218, and 200 nm have been investigated experimentally. The quantum-mechanical calculations of the intensity distribution in the resonance Raman spectra of three adenine tautomers are performed in the Herzberg-Teller approximation with the inclusion of the Duschinsky and frequency effects. Conclusions regarding the tautomeric composition of adenine in the gas phase are drawn from comparison of the results of quantum-mechanical calculations with experimental data.

Quantum-mechanical calculation of the intensity distribution in the resonance Raman spectrum of benzonitrile

A direct quantum-mechanical calculation of the resonance Raman spectrum of a benzonitrile molecule upon excitation with laser radiation at a wavelength of 228.7 nm is performed in the Herzberg-Teller approximation with allowance made for the Duschinsky effect. The results of the calculation are in reasonable agreement with the available experimental data. The intensity distribution in the calculated resonance Raman spectrum of the benzonitrile molecule is compared with the intensity distributions in the spectra of benzene, methyl-substituted benzenes, and halogenated benzenes. It is revealed that the intensity distributions in the resonance Raman spectra of these compounds are characterized by a number of common features.

Quantum mechanical analysis of the intensity distribution in spectra of resonant hyper-Raman scattering of polyatomic molecules

The quantum-mechanical approach and the method of calculation of the relative intensities of lines of polyatomic molecules, which were previously applied to the analysis of their vibronic absorption and resonant Raman scattering spectra, are assumed to be extended to the description of the intensity distributions in spectra of resonant hyper-Raman scattering of such molecules. This will make it possible to describe all these spectra from the same viewpoint in accordance with their similar physical nature based on a common set of parameters. The basic stages and particular features of the implementation of the method are discussed, and the intensity distribution in the spectrum of resonant hyper-Raman scattering of fluorobenzene is calculated. A comparison of the calculation results with the experimental data indicates that it is expedient to analyze the intensity distributions in the spectra of resonant hyper-Raman scattering of polyatomic molecules using the quantum-mechanical method.

Quantum-mechanical calculation of the intensity distribution in resonance Raman spectra of cytosine

A quantum-mechanical calculation of the relative intensities of lines in resonance Raman (RR) spectra of cytosine excited by laser radiation at 266, 218, and 200 nm was performed in different approximations of the vibronic theory. Both the Herzberg-Teller effect and the contribution from electronic states located close to the resonance state are shown to play a significant role in determining the relative intensities of lines. A satisfactory agreement between the calculated results and experimental data is obtained. The specific features of the intensity distribution in the RR spectra of cytosine are compared with those in the spectra of the previously studied thymine and uracil, which have a similar structure and also belong to the simplest nucleic acid bases.

Quantum mechanical analysis of resonance Raman spectra of thymine

A direct quantum mechanical calculation of the relative intensities of lines in resonance Raman (RR) spectra of thymine was performed. The method of calculation is based on the adiabatic model in the Herzberg-Teller approximation. It is shown that the basic features of the intensity distribution in the spectra can be explained only by taking into account the vibronic mixing of electronic states and the contribution to the components of the scattering tensor from excited electronic states located close to the resonance state. The calculated results agree satisfactorily with experimental RR spectra of thymine excited by laser radiation at 266, 240, 218, and 200 nm. A comparative analysis of the intensity distribution in the RR spectra of thymine and uracil is carried out.

Quantum-Mechanical Analysis of Resonance Raman Scattering Spectra of the Uracil Molecule

A direct quantum-mechanical calculation of the relative intensities of lines in the resonance Raman scattering (RRS) spectra of uracil is performed by a method developed earlier by the authors on the basis of the adiabatic model in the Herzberg-Teller approximation [1]. It is shown that the main regularities in the intensity distribution of spectra can be explained only by taking into account the vibronic mixing of electronic states and the contribution to the scattering tensor components from the excited electronic states adjacent to the resonance state. The calculated results are in satisfactory agreement with the results of experimental studies of the RRS spectra of uracil excited by laser radiation at 266, 240, 218, and 200 nm.

Theoretical analysis of the structure of excited electronic states, Raman, and resonance Raman spectra of indole in the isolated state and aqueous solution

The structure of the first excited electronic states of indole has been calculated for the isolated state and aqueous solution. The vibrational spectra of isolated indole have been calculated by the DFT method in the harmonic and anharmonic approximations. The resonance Raman spectra of indole have been calculated quantum mechanically in the Herzberg-Teller approximation. The effect of hydrogen bonds on the structure and vibrational (Raman and resonance Raman) spectra of indole has been analyzed.

Quantum-mechanical calculation of the intensity distributions in spectra of resonance hyper-Raman scattering and two-photon absorption of indole and skatole

We have performed a quantum-mechanical calculation of the relative intensities of lines in the spectra of resonance hyper-Raman scattering and two-photon absorption of isolated indole, indole in an aqueous solution, isolated skatole, and skatole-water complex. The effects of hydrogen bonds and intermolecular interaction on the spectra have been considered. Particular features of the intensity distributions in the spectra of indole and skatole have been compared.