ИСТИНА

Presently the structures of about 9000 molecules have been determined by experimental methods, mainly by gas electron diffraction (ED) and rotational spectroscopy. Most of these structures, namely ra, rg, r0, rs etc., are averaged being dependent on vibrational, rovibrational and other effects. However, for a correct comparison and combined use of data from different methods, they should have the same physical meaning. Therefore, in our benchmark studies, the equilibrium structures of several molecules, namely, of uracil [1], 1-methyluracil [2], thymine [3,4], 1-methylthymine [5] and others [6-8], have been derived from microwave (MW) rotational constants and/or ED data taking into account rovibrational or vibrational corrections calculated from ab initio anharmonic force fields. Furthermore, the accurate equilibrium structures of these molecules have been computed by the CCSD(T)/cc-pwCVTZ(ae) method with extrapolation to the higher (quadruple-zeta) basis set at the MP2 level. A remarkable agreement between the computed (re(best ab initio)) and semi-experimental equilibrium (re ) structures points to a high accuracy of both experiment and applied theory. On the other hand, the large discrepancies between the re and averaged (ra and rs, see Fig. 1) structures point to strong distortion of the experimental data due to vibrational effects. [1] N. Vogt, L.S. Khaikin, et al., J. Mol. Struct., 2013, 1050, 114-121. [2] N. Vogt, I.I. Marochkin, et al., J. Phys. Chem. A, 2013, 117, 11374-11381. [3] N. Vogt, J. Demaison, et al., J. Mol. Struct., 2014, 1076, 483-489. [4] N. Vogt, L.S. Khaikin, et al., J. Phys. Chem. A 2009, 113, 931-937. [5] N. Vogt, I.I. Marochkin, et al., J. Phys. Chem. A, 2015, 119, 152. [6] N. Vogt, E.P. Altova, et al., Struct. Chem, 2015, 26, 1481-1488. [7] N. Vogt, J. Demaison, et al., PCCP, 2015, in press. [8] N. Vogt, J. Demaison, et al., Struct. Chem, 2011, 22, 337-343.