Application of Synchrotron Radiation to Analyze the Friction-Induced Structural and Phase Transformations of Chrome-Nickel Austenitic Steel

Russian Physics Journal -     

Ab initio study of the structure and conformations of 2-fluoroethanal in the ground and lowest excited electronic states

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.     

Molecular Structure and Conformations of Chloral (CCl3CHO) in the Ground and Lowest Triplet States

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.     

Ab initio study of the structure of 2,2-difluoroethanal in the ground and lowest excited triplet electronic states

The molecular structure of 2,2-difluoroethanal (DFE) in the ground (S₀) and lowest excited triplet (T_i) electronic states was investigated byab initio quantum-chemical methods. In the S₀ state, the DFE molecule exists as the only stablecis conformer. The T_i↓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 T_i 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.     

Features of the fluorine‐substituted acetaldehydes dynamics in the low‐lying electronic states: Quantum mechanical study of the CHF2CHO molecule lowest excited singlet state

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 CCH_aO 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     

Structure and conformational dynamics of the dicyclopropyl ketone in the ground electronic state

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.     

The S1 ← S0 vibronic spectra and structure of the (CH3)2 CHCHO and (CH3)2 CHCDO 2-methylpropanal molecules

A multipass cell with an optical path up to 120 m long was used to measure the vibronic absorption spectra of 2-methylpropanal-h₁ (MPA-h₁, (CH₃)₂CHCHO)) and 2-methylpropanal-d₁ (MPA-d₁, (CH₃)₂CHCDO)) over the frequency range 28200–31600 cm⁻¹. The most intense spectral lines were assigned to transitions from vibrational levels of the cis and gauche MPA-h₁ and MPA-d₁ conformers in the ground electronic state (S ₀) to vibrational levels of conformers 1 and 3 in the lowest singlet excited electronic state (S ₁). According to our estimates, the origins (0 ₀ ⁰ ) of the 1 S ₁) ← cis(S ₀) and 3(S ₁) ← cis(S ₀) and also 1(S ₁) ← gauche(S ₀) and 3(S ₁) ← gauche(S ₀) electronic transitions were situated at 29147 and 29177, 29391 and 29417 cm⁻¹, respectively, for MPA-h₁ and at 29226 and 29240, 29480 and 29500 cm⁻¹ for MPA-d₁. The structure of conformers 1 and 3 in the S ₁ state was shown to differ from the structure of the cis and gauche conformers in the S ₀ state by the angle of rotation of the (CH₃)₂CH-isopropyl top and “pyramidal distortion” of the CCHO/CCDO carbonyl fragment. A series of fundamental frequencies of MPA conformers in different electronic states were found. The potential functions of inversion were determined for the conformer 1-conformer 3 pairs of MPA-h₁ and MPA-d₁ from the experimental energy levels of inversion vibrations. The potential barriers to inversion and equilibrium displacements of the CH/CD bond out of the CCO plane were found to be 735/675 cm⁻¹ and ±34°/±32° for MPA-h₁ and MPA-d₁, respectively. Original Russian Text ? I.A. Godunov, S.L. Lur’e, N.N. Yakovlev, V.A. Bataev, 2007, published in Zhurnal Fizicheskoi Khimii, 2007, Vol. 81, No. 1, pp. 52–62.     

Ab initio Quantum-Mechanical Calculations of Molecular Structure and Conformations of 2,2-Dichloroethanal in the Ground and Excited Lowest Triplet States

Ab initio calculations were carried out to investigate the molecular structure of 2,2-dichloroethanal (DCE, CHCl₂CHO) in the ground (S ₀) and excited lowest triplet (₁) states. It is found that electronic excitation of DCE from the S ₀ to T ₁ state occurs with top rotations and a loss of planarity of the carbonyl fragments. Six minima corresponding to three pairs of enantiomers were found on the potential energy surface (PES) of the DCE molecule in the ₁ state. Based on the PES calculated (by the UHF and CASSCF methods in a 6-31G** basis) for DCE in the ₁ state, the one-dimensional torsional and inversion problems and the two-dimensional torsional-inversion problems are solved. A comparison of the results has revealed a relationship between the torsional and inversion motions.     

Potential functions of inversion of R2CO (R=H, F, Cl) molecules in the lowest excited electronic states

The inversion potentials of R₂CO (R=H, F, Cl) molecules in the lowest excited electronic states were determined from experimental data using various model potential functions and approximations for the kinetic energy operator of inversion motion. The estimates of the heights of the barriers to inversion and the equilibrium values of the inversion coordinate for the H₂CO molecule in the S₁ and T₁ states are fairly stable. The results for the F₂CO and Cl₂CO molecules are strongly dependent on the approximation used; for these molecules, the most reliable parameters of the potential functions were chosen. The problem of qualitative characteristics of the shape of inversion potentials is discussed using the results ofab initio quantum-chemical calculations of the molecules under study. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 645–651, April, 1999.