A quantum chemical study of the structure of fluorinated silver acetate(I) monomers and dimers

Quantum chemical calculations of the equilibrium structure, potential energy surface cross-sections along the nonrigid degrees of freedom of (CF₃COOAg)₂, (CHF₂COOAg)₂, (CH₂FCOOAg)₂, and (CH₃COOAg)₂ dimers and the corresponding monomers are presented. The B3LYP method with the augmented cc-pVTZ basis set for C, O, F atoms and the Stuttgart 1997 RSC basis set together with the relativistic effective potential for Ag atoms is used. It is shown that in all dimers the eight-membered ring is a rather rigid planar fragment, and the Ag atoms can be bonded with the bond order of 0.2 in dimers. Almost free rotation of acyclic groups around the C-C bond in (CH₃COOAg)₂ and (CF₃COOAg)₂ dimers transforms into a hindered one in the (CHF₂COOAg)₂ dimer, and further into the existence of syn- and anti-structures divided by a high rotation barrier in the (CH₂FCOOAg)₂ dimer. In monomers, the ratio of the internal rotation barriers is similar. With increasing number of fluorine substitution for hydrogen atoms in dimers the Ag-Ag bond length is found to increase (2.79 Å, 2.81 Å, 2.83 Å, 2.84 Å) and the ring rigidity to simultaneously decrease in the acetate-triflouroacetate series.     

Substance recognition in the open atmosphere from a single Fourier transform spectroradiometer interferogram

An in-situ technique for identification of substances in the open atmosphere from the analysis of a single Fourier-transform spectroradiometer interferogram is described. A database of spectra of major atmospheric constituents and typical atmospheric paths is compiled to be used for the calculation of an atmospheric path with the following separation of a pollutant spectrum from the experimentally recorded spectrum. The identification of a substance by its spectrum is performed through sorting out substances from the database by the correlation coefficients and a quantitative analysis is performed by minimizing the discrepancy functional between the experimental and database spectra. The technique described is tested in situ.     

Processing of double-sided interferograms subject to background self-radiation of an FTIR spectrometer

The effect of background (instrumental) self-radiation of a Fourier transform infrared (FTIR) spectrometer on the processing of double-sided interferograms is studied. From a theoretical analysis of the Michelson interferometer it was shown that when the brightness temperature of the object of study is close to the temperature of the instrument, the measured spectrum may contain inverted spectral ranges or isolated bands. The interferogram correction algorithms and experimental technique for elimination of the spectrum inversion and for compensation of the background self-radiation of the instrument are suggested.     

Interactive software for experimental data analysis and problem solving in vibrational spectroscopy

Translated from Programmno-Apparatnye Sredstva i Matematicheskoe Obespechenie Vyschislitel'nykh Sistem, pp. 160–169, Izd. Moskovskogo Universiteta, Moscow, 1989.     

On determination of the response characteristics of detectors used in gas electron diffraction

The methods of determining and taking into account the nonlinearity of the response characteristics of photographic materials used in gas electron diffraction experiments are considered. A technique is proposed that yields reliable characteristics of the nonlinearity of photographic materials based on the instrumental background of an electron diffraction apparatus measured at multiple exposure times. Experiments are carried out and the response curve of the photo emulsion of KODAK SO-193 used in the electron diffraction laboratory of the Chemistry Department of MSU is determined. The developed technique can be applied to determine the response characteristics of various registering devices.     

Theory and calculations of second-order anharmonic corrections to the radial distribution function of polyatomic molecules

A theory of the thermal averages of normal coordinates was suggested for polyatomic molecules. Second-order approximation equations were obtained on the basis of iterations of the Bloch integral equation. These equations can be used to calculate anharmonic corrections to the radial distribution function and the parameters that determine the intensity of fast electron scattering by molecules in gas-phase electron diffraction.     

Calculation of instrumental functions as a method for analyzing the alignment of the IR channel of a scanning Fourier-transform IR spectroradiometer

Optics and Spectroscopy - A specific feature of scanning Fourier-transform IR spectroradiometers (FTIR SRs) is the use of a multiarea photodetector. The optical scheme of these SRs is calculated so...     

Internal rotation and equilibrium structure of the 2-methyl-2-nitropropane molecule from joint processing of gas phase electron diffraction data,vibrational and microwave spectroscopy data,and quantum chemical calculation results

The structure and internal rotation of the 2-methyl-2-nitropropane molecule is studied by electron diffraction and quantum chemical calculations with the use of microwave and vibrational spectroscopy data. The electron diffraction data are analyzed within the general intramolecular anharmonic force field model and the quantum chemical pseudoconformer model, considering the adiabatic separation of the degree of freedom of large amplitude motion, i.e., the internal rotation of the NO₂ group. The equilibrium eclipsed configuration of the C _s symmetry molecule has the following experimental bond lengths and valence angles: r _e(N=O) = 1.226//1.226(8) Å, r _e(C–N)//r _e(C–C) = 1.520//1.515/1,521(4) Å, ∠_еC–C–N = = 109.1/106,1(8)°, ∠_еO=N=O = 124.2(6)°, ∠_eC–C–H_avg = 110(3)°. The equilibrium geometry parameters are well consistent with MP2/cc-pVTZ quantum chemical calculations and microwave spectroscopy data. The thermally average parameters previously obtained within the small vibration model show a satisfactory agreement with the new results. The electron diffraction data used in this work do not allow a reliable determination of the barrier to internal rotation. However, at a barrier of 203(2) cal/mol, which is derived from the microwave study, it follows from the electron diffraction data that the equilibrium configuration must correspond to an eclipsed arrangement of C–C and N=O bonds, which is also consistent with the results of quantum chemical calculations of various levels.     

Hexamethylenetetramine (urotropine) C6H12N2: Interpreting the vibrational spectra of -d0 and -d12 isotopomers by scaling the quantum-chemical force field

The equilibrium structure and quadratic and cubic force fields of the urotropine molecule are calculated at the MP2 (full)/cc-pVTZ level. Pulay scaling of the quadratic force field allows unambiguous interpretation of the vibrational spectra of -d₀ and -d₁₂ urotropines. A reliable matrix for the quadratic force constants of urotropine is obtained which may be used to determine the parameters of the equilibrium structure of the urotropine molecule by means of gas-phase electron diffraction.     

Design of the optimal sector device and determination of its parameters in gas electron diffraction

This work presents a way to select the optimal form of the sector lobe and practical algorithms to determine the sector function of the device in use. Knowledge of the sector function enhances the quality of drawing a background line and ensures the division of multiplicative and additive noise components, thus increasing the reliability of structural parameters determined by gas electron diffraction.