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Theoretical study of the structure of the CClF2NO and CCl2FNO molecules in the ground and lowest excited singlet and triplet electronic states

The potential energy surfaces of the nitroso compounds CClF2NO and CCl2FNO in the ground and lowest excited singlet and triplet electronic states were studied by various ab initio methods (including multiconfigurational methods). The equilibrium geometric parameters, vibrational frequencies, internal rotation potential functions, and rotational contours of bands in the S1 ← S0 vibronic spectrum of the CClF2NO molecule were calculated. For the molecules under consideration, the quantum-mechanical problem on torsional motion was solved. The results of calculations are, on the whole, in good agreement with experiment.

S1←S0 Vibronic spectrum and structure of 2,2-difluoroethanal in the S1 state

The vibronic spectrum of the 2,2-difluoroethanal vapor was recorded using a multipass optical cell with an optical length of at least 140 m. The spectrum in the region of 300—364 nm was assigned to the S1←S0 electronic transition (from the ground S0 to the first excited singlet S1 electronic state); the vibrational structure of the spectrum was analyzed. The spectrum bands were assigned to two systems of vibronic transitions, namely, transitions between the levels of the cis-conformer (S0) and of the S1 conformers, with the origins (000 transitions between the zero vibrational levels of conformers) at 29192 and 29087 cm–1, respectively. Analysis of the spectrum showed that the S1←S0 electronic excitation of the cis-conformer was followed by rotation of the CHF2 top and pyramidal distortion of the carbonyl fragment. A number of fundamental frequencies were found for S1 conformers, in particular, torsion and inversion energy levels. The experimental data are in satisfactory agreement with the results of quantum-chemical calculations for the 2,2-difluoroethanal molecule in the S0 and S1 states.

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 (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.

The structure of CX2YNO (X, Y=F, Cl) molecules in the ground and lowest excited singlet electronic states

Ab initio quantum-chemical calculations of equilibrium geometric parameters, vibrational frequencies, and potentials of internal rotation for CCIF2NO and CCl2FNO molecules in the ground (S0) and lowest excited singlet (S1) electronic states were performed. The results of calculations were compared with experimental data. A new interpretation of experimental spectra of the CCIF2NO molecule was suggested.