Quantum-chemical study of the structure of copper(I) acetate and trifluoroacetate oligomers

The results of B3LYP quantum-chemical calculations of the equilibrium structures of [(CX₃COOCu)₂]₃, [(CX₃COOCu)₂]₂, and (CX₃COOCu)₂ oligomers (X = H, F) using the cc-pVTZ correlation-consistent basis for C, O, and F atoms and the Stuttgart 1997 RSC basis and relativistic effective core potential for Cu(I) atoms are presented. The differences in the structures of the free dimer and dimer units in oligomers were studied. The hexamer structure was chosen as the model of a fragment of the crystalline phase. Good agreement was obtained between the experimental and calculated differences between the geometrical parameters of the structures in the “gas phase-crystal” and “acetate-trifluoroacetate” series. Based on the calculated data, the increase in the Cu(I)-Cu(I) bond length in the silver acetate crystal compared with the gas phase can be explained by the effect of the neighboring dimer units of the polymer ribbon, while the increase in the Cu(I)-Cu(I) bond length in gaseous trifluoroacetate compared with acetate, by the acceptor effect of fluorine atoms.     

An error self-compensation mechanism for deposition of optical coatings with broadband optical monitoring

An error self-compensation mechanism is investigated for use during the deposition of optical coatings with broadband optical monitoring. The correlation of thickness errors caused by monitoring procedure is mathematically described. It is shown that this correlation of errors may result in the effect of selfcompensation of errors.     

Spatial and temporal effects upon deposition of particles onto thin films of silicon dioxide produced using high-energy deposition processes

The interaction of deposited atoms with a silicon dioxide film is simulated for the case of using high-energy processes for the deposition of optical nanocoatings. The method of molecular dynamics with a classical force field is used for describing the interaction between the atoms. The characteristic time of fast relaxation of the kinetic energy of the deposited atom and the characteristic depth of its penetration into the film are estimated. It is shown that the angular distribution of the velocities of the deposited atoms is significant for the formation of a coating.     

The equilibrium molecular structure of 3-cyanopyridine according to gas-phase electron diffraction and microwave data and the results of quantum-chemical calculations

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Extraneous scattering and its discrimination in gas electron diffraction

The division algorithm for additive and multiplicative noise components of the electron scattering intensity is proposed in the work. The procedure presented provides a substantial improvement in experimental data processing in comparison with the traditional method used by Russian research groups. A comparison of the additive noise with the simulated residual gas scattering shows that it is this scattering that is largely responsible for the strange contribution to the measured diffraction pattern.     

Modification of Graphene on a Copper Grid during Femtosecond Laser Irradiation: Electron Diffraction and Raman Spectroscopy Studies

The initial stage of a nanosecond discharge in gaps with a high electric field at a cathode is studied by laser methods (interferometric, shadow, schlieren methods). The studies are performed in air at atmospheric pressure. Prominence is given to studying the evolution (appearance and growth) of the plasma channels at an anode and to estimating their parameters.     

Internal Rotation and Equilibrium Structure of the Bromonitromethane Molecule According to Gas Electron Diffraction Data and Quantum Chemical Calculations

The structure and internal rotation of the bromonitromethane molecule are studied using electron diffraction analysis and quantum chemical calculations. The electron diffraction data are analyzed within the models of a general intramolecular anharmonic force field and quantum chemical pseudoconformers to account for the adiabatic separation of a large amplitude motion associated with the internal rotation of the NO₂ group. The following experimental bond lengths and valence angles are obtained for the equilibrium orthogonal configuration of the molecule with C_s symmetry: r_e(N=O) = 1.217(5) Å, r_e(C–N) = 1.48(2) Å, r_e(C–Br) = 1.919(5) Å, ∠_еBr–C–N = 109.6(9)°, ∠_еO=N=O = 125.9(9)°. The equilibrium geometry parameters are in good agreement with CCSD(T)/cc-pVTZ calculations. Thermally averaged parameters are calculated using the equilibrium geometry and quadratic and cubic quantum chemical force constants. The barrier to internal rotation cannot be determined reliably based on the electron diffraction data used in this work. There is a 82% probability that the equilibrium configuration with orthogonal C–Br and N=O bonds is most preferable, and internal rotation barrier does not exceed 280 cm^-1, which agrees with CCSD(T)/cc-pVTZ calculations.     

Calculation of Second- and Higher-Order Force Constants Including Electron Correlation Effects and Hartree-Fock Force Constant Scaling

A formalism suitable for practical implementation is suggested for computation of quadratic, cubic, and quartic force constants using the configuration interaction (CI) method. Expressions are compared which involve the Hartree-Fock (HF) harmonic and anharmonic force constants calculated by the HF and CI methods. Also, physical assumptions are formulated to perform scaling of the diagonal harmonic and, which is more important, of anharmonic HF force constants with a common scaling factor. This approach is consistent with the data of ab initio quantum-chemical calculations. A table is presented which compares the results of valence force constant calculations for a series of simple organic molecules.     

Modeling of scattering on the residual gas in an electron diffraction experiment

The scattering on the residual gas in an electron diffraction chamber is modeled. A comparison with experimental data reveals that is this scattering that may make a major contribution to the extraneous signal inevitably present in the recorded diffraction pattern. Practical recommendations on the development of the electron diffraction apparatus design are given.     

Equilibrium Structure and Internal Rotation in B2F4 from Electron Diffraction and Spectroscopic Data and Quantum Chemical Calculations

Electron diffraction (ED) data for B₂F₄ recorded by Hedberg et al. over the temperature range –80 to +150°C have been used to obtain equilibrium geometry of this molecule in the framework of a large-amplitude motion model. The torsional coordinate has been adiabatically separated from the rest of vibrations. Two types of constraints applied to obtain ab initio torsional potential energy function (PEF) and the parameters of the geometry relaxation are discussed. The relations between anharmonic interaction force constants and the parameters of the geometry relaxation are briefly considered. Ab initio force constant matrices for rigid vibrational coordinates as well as large-amplitude torsional PEF have been scaled in the procedure of simultaneous fitting to the ED data and experimental vibrational frequencies. The resulting equilibrium geometry and potential function provided good fit to both ED and spectroscopic data. As expected, the results for the equilibrium geometry obtained from separate ED patterns recorded at different temperatures did not show noticeable temperature trend. The determined equilibrium structural parameters for B₂F₄ are: r _e (B–B) = 1.719(4) Å, r _e (B–F) = 1.309(2) Å, BBF = 121.1(1)°. Uncertainties given in parentheses include three times standard deviation and a systematic error. The rotational barrier height was evaluated as 160(50) cm^–1.