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1.
Yu. N. Pachenko V. I. Pupyshev A. V. Abramenkov 《Journal of Molecular Structure》1985,130(3-4):355-359
Ab initio computations of the potential energy curve of internal rotation around the central single C---C bond of isoprene have been performed at the Hartree—Fock level with a 3·21G basis set. The similarity of the slope of the curve obtained and the potential energy curve calculated for a more complete basis set (7s3p/4s2p) [Kavana-S2ebø, J. Mol. Struct. 106 (1984) 259] is discussed. The values of the Pitzer function F(φ), its Fourier expansion coefficients, and coefficients of the potential energy expansion were calculated from data given in the above reference. The correction of the potential energy expansion coefficients was carried out from frequencies of torsional “hot” bands of isoprene and torsional overtone of its second rotational isometric form. It was shown that the isoprene second isomer is realized as a gauche-form. The potential energy expansion coefficients were obtained as follows: V1 = 399.9, V2 = 1330.22, V3 = 781.8 and V4 = −175.8 cm−1. 相似文献
2.
The results of the analysis of the fluorescence excitation spectrum of trans-hexafluorobiacetyl published earlier are revised.
New values of torsion frequencies and potential barriers of internal rotation of the CF3 group in the ground and excited states of the molecule are obtained. A procedure for calculating the probabilities of torsional
vibronic transitions of molecules is described.
Translated fromZhurnal Struktumoi Khirnii, Vol. 38, No. 2, pp. 293–302, March–April, 1997. 相似文献
3.
The structure of the conformationally flexible 2-fluoroethanal molecule (CH2FCHO, FE) in the ground (S0) and lowest excited triplet (T1) and singlet (S1) electronic states was investigated by ab initio quantum-chemical methods. The FE molecule in the S0 state was found to exist as two conformers, viz., as cis (the F—C—C—O angle is 0°) and trans (the F—C—C—O angle is 180°) conformers. On going both to the T1 and S1 states, the FE molecule undergoes substantial structural changes, in particular, the CH2F top is rotated with respect to the core and the carbonyl CCHO fragment becomes nonplanar. The potential energy surfaces for the T1 and S1 states are qualitatively similar, viz., six minima in each of the excited states of FE correspond to three pairs of mirror-symmetrical conformers. Based on the potential energy surfaces calculated for the FE molecule in the T1 and S1 states, the one-dimensional problems on the torsion and inversion nuclear motions as well as the two-dimensional torsion-inversion problems were solved. 相似文献
4.
V. A. Bataev E. K. Dolgov A. V. Abramenkov G. M. Kuramshina I. A. Godunov 《Russian Chemical Bulletin》2000,49(6):984-990
The molecular structure of 2,2-difluoroethanal (DFE) in the ground (S0) and lowest excited triplet (Ti) electronic states was investigated byab initio quantum-chemical methods. In the S0 state, the DFE molecule exists as the only stablecis conformer. The Ti↓S0 electronic excitation is accompanied by the rotation of the top and the deviation of the carbonyl fragment from planarity.
For the DFE molecule in the Ti state, six minima corresponding to three pairs of enantiomers were found on the potential energy surface. Based on this potential
energy surface, the problems on torsion and inversion nuclear motions were solved in the one- and two-dimensional approximations,
and the interaction between these motions was revealed.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 989–995, June, 2000. 相似文献
5.
Yurii N. Panchenko Charles W. Bock Joseph D. Larkin Alexander V. Abramenkov 《Structural chemistry》2008,19(5):793-799
In connection with the appearance of new experimental vibrational data on the high-energy rotational isomer of 2,3-dimethylbuta-1,3-diene
(I) in a low-temperature matrix and in neat crystals, the ab initio-based vibrational analysis of this molecule has been re-evaluated.
Calculated wavenumbers derived from a scaled quantum-mechanical force field analysis at the MP2(FC)/aug-cc-pVDZ//MP2(FC)/aug-cc-pVDZ
computational level are compared with experimental data. Several reassignments of the fundamental wavenumbers for I have been suggested in the course of the current analysis, and the existence of a high-energy non-planar s-gauche conformer of 2,3-dimethylbuta-1,3-diene has been confirmed. 相似文献
6.
Various approximations of the method of determining two-well potential functions of molecular inversion from experimental
data (geometrical parameters and inversion level energies) are considered. The potential of the method is illustrated by reference
to carbonyl molecules in the lowest excited states. Some of the current problems are discussed.
Translated fromZhurnal Strukturnoi Khimii, Vol. 39, No. 5, pp. 947–961, September–October, 1998 相似文献
7.
8.
V. A. Bataev M. N. Mikhailov A. V. Abramenkov V. I. Pupyshev I. A. Godunov 《Journal of Structural Chemistry》2001,42(1):57-65
This paper reports on an ab initio quantum mechanical calculation of the structure of the conformationally nonrigid chloral (CCl3CHO) molecule in the ground (S0) and lowest excited triplet (T1) states. Electronic excitation causes substantial changes in molecular geometry: the CCl3 top is rotated, and the carbonyl (CCHO) fragment becomes nonplanar. For the torsional (S0 and T1) and inversion (T1) nuclear vibrations, one- (S0 and T1) and two-dimensional (T1) vibrational problems are solved; a relationship is found between the torsional and inversion vibrations in the T1 state. The results are compared with the data of analogous calculations for the acetaldehyde molecule in the T1 state. 相似文献
9.
Ekaterina V. Rastoltseva Vadim A. Bataev Alexander V. Abramenkov Vladimir I. Pupyshev Igor A. Godunov 《Journal of Molecular Structure》2010,939(1-3):14-21
Geometric parameters, harmonic and anharmonic vibrational frequencies, conformer energy differences and barriers to internal rotation were obtained for dicyclopropyl ketone (DCPK) in the ground electronic state through MP2, DFT, CCSD and CCSD(T) calculations. VFPA was used to improve the estimations of conformer energy differences and heights of barriers to internal rotation. The ab initio calculations demonstrated that there are three stable conformations of DCPK: the cis–cis, the cis–trans and the gauche–gauche. The energy of the gauche–gauche conformer is noticeably higher than the energy of the two other conformers, so this conformer was not found experimentally. To study the conformational dynamics of the DCPK molecule, one- and two-dimensional sections of the potential energy surface corresponding to the rotations of the cyclopropyl groups were calculated. These sections were used to calculate torsion transition energies and vibrational wave functions in anharmonic approach. It was found that there is a strong coupling of large-amplitude torsion motions in the area of the cis–cis and gauche–gauche conformers. 相似文献
10.
Vadim A. Bataev Eugeniy K. Dolgov Alexandr V. Abramenkov Vladimir I. Pupyshev Igor A. Godunov 《International journal of quantum chemistry》2002,88(4):414-425
The potential energy surface (PES) for the CHF2CHO molecule in the excited S1 state is calculated by the CASSCF method. The features of the 1‐ and 2‐D cross‐sections of PES are considered in comparison with those of the relative molecules. The vibrational frequencies are calculated in harmonic approximation and the vibrational energy levels for the inversion motion of the carbonyl fragment CCHaO and for the torsion motion of the CHF2‐top are calculated in anharmonic approximation by the 1‐ and 2‐D variational methods. The calculated data are compared with the experimental ones. The problems of the experimental data interpretation are considered. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002 相似文献