NATURAL SCIENCES

Journal of fundamental
and
applied researches

Structural-dynamics models of isomersformic acid in the condensed states

2013. №2, pp. 195-202

Elkin Mihail D.  - D.Sc. (Physics and Mathematics), Professor, Astrakhan State University, 20a Tatishchev St., Astrakhan, 414056, Russian Federation, elkinmd@mail.ru

Testova (Nuralieva) Diana M. - post-graduate student, Astrakhan State University, 20aTatishchev St., Astrakhan, 414056, Russian Federation, dianet_88@mail.ru

Likhter Anatoliy M.  - D.Sc. (Technical Sciences), Associate Professor, Astrakhan State University, 20a Tatishchev St., Astrakhan, 414056, Russian Federation, kof@aspu.ru

Kolomin Valentin I.  - D.Sc. (Pedagogical Sciences), Associate Professor, Astrakhan State University, 20a Tatishchev St., Astrakhan, 414056, Russian Federation, estnauki2009@rambler.ru

Grechukhina Oksana N.  - Ph.D. (Physics and Mathematics), Associate Professor, Astrakhan State University, 20a Tatishchev St., Astrakhan, 414056, Russian Federation, kof@aspu.ru

The successful solution of the problem of interpretation of a complex contour bands in the high-frequency range of the vibrational spectrum of carboxylic acids based on adequately the structural and dynamic models, in particular, one of the simplest models of this class – formic acid (UA). The theoretical basis for the interpretation of the vibrational states are quantum methods for assessing the parameters of the adiabatic potential (force constant), but the results obtained may differ depending on the basis of the calculation, and, for example, formic acid, with the conformers of molecular objects about ten, and therefore the details of the spectral identification of the representation in this work is very important. Model calculations are carried out within the framework of the density functional method DFT/B3 LYP using bases 6-311G*, 6-311G**, 6-311+G**. This approach has enabled to clarify the influence of polarization and diffusion parameters of the basis for the results of the calculation. It is shown that the interpretation of the fundamental vibrations of the MC does not affect the choice of basis in view of the large size of the gap between the values of frequencies, while for cyclic dimers – the more complex of the class of carbon-nucleic acids – the energy gap between the frequencies interpreted as vibrations of the OH bond and CH should be considered. Found that the mechanism of dimer formation MK is hydrogen bond and calculated the parameters, such as the cyclic dimer (A) estimate of the length of the hydrogen bond (O---H) gave a value of ~1.68–1.75 ?, and for the non-cyclic dimer was obtained: B1(1.80 and 2.37), B2 (1.78 and 2.31), C1 (1.96 and 1.95), C2 (1.85 and 1.92); D (1.90 and 2.43); E1(2.47), E2 (2.41), E3 (2.38); F1 (2.59 and 2.43), F2 (2.56 and 2.39), and the effect of basis does not exceed the value vysilo 0.05 ?, suggesting that the weak and strong hydrogen bond in dimers MC.

Key words: structural and dynamic models,isomers,formic acid,condensed state,the adiabatic potential,vibrational states,identification