Quantum-chemical study of the structure of the acetyl fluoride molecule in the ground and lowest excited singlet and triplet electronic states

The structure of the conformationally flexible acetyl fluoride molecule (CH3CFO and CD3CFO) in the ground (S0) and lowest excited triplet (T1) and singlet (S1) electronic states was calculated by different quantum-chemical methods (RHF, UHF, MP2, CASSCF). The equilibrium geometric parameters and harmonic vibrational frequencies of the molecules in these electronic states were estimated. The calculations demonstrated that the electronic excitation causes considerable conformational changes involving the rotation of the CH3(CD3) top and a substantial deviation of the CCFO carbonyl fragment from planarity. For large-amplitude vibrations, namely, for the torsional vibration in the S0 state and the torsional and inversion (nonplanar carbonyl fragment) vibrations in the T1 and S1 states, the quantum-mechanical problems were solved in one-dimensional (1D) and two-dimensional (2D) approximations. The results of calculations are in good agreement with experimental data.     

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.     

Verification of boundedness for the powers of symplectic matrices with the help of averaging

Novosibirsk. Translated fromSibirski Matematicheski Zhurnal, Vol. 33, No. 6, pp. 3–13, November–December, 1992.     

Use of relaxation viscoelastic model in calculating uniaxial homogeneous strains and refining the interpolation equations for maxwellian viscosity

The work applies the relaxation viscoelastic model proposed in [1–3] for calculations of high-rate deformation of bars and plates and for refining the interpolation equations of Maxwellian viscosity χ (a magnitude inverse to the relaxation time τ of the tangential stresses) by means of them. These calculations were carried out to study the dependence of the dynamic yield limit σ_g on the deformation rate ?^·. The authors propose that the dependence σ_g(?, T) in ?^· be transformed, such that χ = ?^· (σ, T) (here σ is the intensity of the tangential stresses and T is temperature) in order to construct interpolation equations for Maxwellian viscosity χ. A numerical analysis demonstrated that this equation leads to the correct qualitative dependence in calculations of σ_g (?^·). A correction factor is introduced into the equation χ = χ(σ, T) in order for the numerical calculations to quantitatively coincide with the experimental data in this work.     

Vibronic spectra and S1 excited electronic state molecular structures for acetyl chloride and acetyl fluoride

Vapor-state absorption spectra have been recorded for acetyl fluoride and acetyl chloride and also for deuterated derivatives with path lengths up to 40 m. The origins of the S₁S₀ transitions have been derived, together with the torsional-vibration energy levels in the ground state S₀ and excited singlet state S₁. Fitting the calculated and observed rotational contours of the vibronic bands has been used to estimate the geometrical parameters in the S₁ states. The carbonyl groups in the S₁ states are nonplanar. The internal-rotation potentials have been determined for acetyl fluoride and acetyl chloride in the S₁ and S₀ states. The relative intensities of the torsional transitions in those states indicate that the minima in the potential energy are appreciably displaced along the torsional coordinate in the S₀ and S₁ states.Chemical Faculty, Lomonosov Moscow University. Translated from Zhurnal Strukturnoi Khimii, Vol. 34, No. 1, pp. 26–30, January–February, 1993.     

Vibronic spectra, ab initio calculations, and structures of conformationally non-rigid molecules of oxalyl halides in the ground and lowest excited electronic states. Part III: Theoretical investigation of oxalyl fluoride

We present a theoretical investigation of oxalyl fluoride (COF)₂ in the ground and the four lowest excited (two singlet and two triplet) electronic states of the n,π∗-type mainly with the CASPT2(8-6)/cc-pVTZ method. Geometries, vibrational frequencies, potential energy functions of internal rotation, and adiabatic electronic transition energies were obtained. The conformer energy difference and the barrier to internal rotation in the ground electronic state were extrapolated to the complete basis set limit. The planar trans and cis conformations were the most stable configurations for all five electronic states under study. We found that the allowed electronic transition of the cis conformer has a transition energy that is significantly higher than that predicted in previous studies. For the excited states, the internal rotation was found to be accompanied by significant non-planar distortion of both carbonyl fragments, indicating strong coupling between these molecular motions.     

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. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1453–1458, August, 1999.     

The Clebsch–Gordan Coefficients with Respect to Various Bases for Unitary and Orthogonal Representations of SU(2) and SO(3)

We calculate the Clebsch–Gordan coefficients for orthogonal rather than unitary representations of the rotation group.     

Interpolation formulas for maxwell viscosity of certain metals as a function of shear-strain intensity and temperature

The purpose of this study is the construction of interpolation formulas for the dependence of Maxwell viscosity, a quantity which is the reciprocal of shear-strain relaxation time , on shear-strain intensity and temperature for several metals: iron, aluminum, copper, and lead. This function was interpolated in various temperature and deformation velocity ranges in accordance with available experimental data for iron (0 10⁷ sec^–1, 200 ° T 1500 °); aluminum (0 10⁷ sec^–1, 300 ° T 900 °); copper (0 10⁵ sec^–1, 300 ° T 1300 °); lead (0 10⁶ sec^–1, 90 ° T 400 °); temperatures in °K.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 4, pp. 114–118, July–August, 1974.