The “Vilkov” issue

INTRODUCTION

The “Vilkov” issue     

Improving the Accuracy of Broad-Band Monitoring of Optical Coating Deposition

A method for improving the accuracy of the broad-band monitoring of the process of depositing optical coatings is proposed. The method is based on determining the actual set of thicknesses of deposited layers in the deposition process. The effectiveness of the proposed approach is demonstrated in a series of model numerical experiments using a simulator of deposition process.     

Electron Diffraction Determination of Equilibrium Structure for Rigid Molecules. Equilibrium Configuration of 1,2-Thiaarsol According to Gas-Phase Electron Diffraction and Quantum-Chemical Data

For rigid polyatomic molecules, a procedure is described for determining their equilibrium geometrical structures by processing gas-phase electron diffraction, spectroscopy, and quantum-chemical data. The efficiency of the procedure is demonstrated by reference to the 1,2-thiaarsol molecule. For this molecule, quantum-chemical calculations of different degrees of complexity have been carried out, and harmonic and anharmonic force fields have been constructed. The force constants were employed for determining the equilibrium geometry from experimental data. Analysis of the results of this study suggests that the calculated vibrational corrections to the internuclear distances are almost independent of the level of the quantum-chemical calculations.Original Russian Text Copyright © 2004 by Yu. I. Tarasov, I. V. Kochikov, D. M. Kovtun, N. Vogt, B. K. Novosadov, and A. S. Saakyan__________Translated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 5, pp. 822–829. September–October, 2004.     

Quantum-chemical calculations for silyl- and alkyl-pseudohalides X3YNCZ (X = H or CH3; Y = C or Si; Z = O,S, or Se) and electron diffraction study of the equilibrium molecular structure of (CH3)3SiNCSe

The equilibrium structures and force fields of the twelve simplest silyl- and alkyl-pseudo halides are calculated by means of B3LYP and MP2(full) quantum-chemical methods with the use of the aug-cc-pVTZ basis. Some regularities in their structure are established. Using these data, the equilibrium structure of the (CH₃)₃SiNCSe molecule with symmetry C _3v is described experimentally for the first time via gas electron diffraction. The following values of the main r _e parameters are determined (uncertainty 3σ is in parentheses): C=Se, 1.709(14) Å; N=C, 1.190(10) Å; N-Si, 1.767(15) Å; Si-C, 1.847(13) Å; N-Si-C, 106.4°; C-Si-C, 112.4°.     

Technique for obtaining and processing spectral information with static fourier spectrometer

We propose a technique and algorithm for processing interferograms obtained with a static Fourier spectrometer. Spectra of secondary radiation from certain compounds are obtained in the visible and near-UV spectral ranges upon excitation by different radiation sources. We present and discuss results of experimental data processing.     

Relativistic Modeling of Ultra-Short Electron Pulse Propagation

Journal of Experimental and Theoretical Physics - The ultrafast electron microscopy, electron diffraction, electron crystallography, and nanocrystallography methods opened the possibility of...     

Observation of coherent optical phonons excited by femtosecond laser radiation in Sb films by ultrafast electron diffraction method

The generation of coherent optical phonons in a polycrystalline antimony film sample has been investigated using femtosecond electron diffraction method. Phonon vibrations have been induced in the Sb sample by the main harmonic of a femtosecond Ti:Sa laser (λ = 800 nm) and probed by a pulsed ultrashort photoelectron beam synchronized with the pump laser. The diffraction patterns recorded at different times relative to the pump laser pulse display oscillations of electron diffraction intensity corresponding to the frequencies of vibrations of optical phonons: totally symmetric (A _1g ) and twofold degenerate (E _g ) phonon modes. The frequencies that correspond to combinations of these phonon modes in the Sb sample have also been experimentally observed.     

Scaled in Cartesian Coordinates Ab Initio Molecular Force Fields of DNA Bases: Application to Canonical Pairs

The model of Regularized Quantum Mechanical Force Field (RQMFF) was applied to the joint treatment of ab initio and experimental vibrational data of the four primary nucleobases using a new algorithm based on the scaling procedure in Cartesian coordinates. The matrix of scaling factors in Cartesian coordinates for the considered molecules includes diagonal elements for all atoms of the molecule and off-diagonal elements for bonded atoms and for some non-bonded atoms (1–3 and some 1–4 interactions). The choice of the model is based on the results of the second-order perturbation analysis of the Fock matrix for uncoupled interactions using the Natural Bond Orbital (NBO) analysis. The scaling factors obtained within this model as a result of solving the inverse problem (regularized Cartesian scale factors) of adenine, cytosine, guanine, and thymine molecules were used to correct the Hessians of the canonical base pairs: adenine–thymine and cytosine–guanine. The proposed procedure is based on the block structure of the scaling matrix for molecular entities with non-covalent interactions, as in the case of DNA base pairs. It allows avoiding introducing internal coordinates (or coordinates of symmetry, local symmetry, etc.) when scaling the force field of a compound of a complex structure with non-covalent H-bonds.     

Electron diffraction study of the equilibrium structure of hexamethylenetetramine involving data from quantum chemistry and vibrational spectroscopy

The equilibrium structure of the urotropine molecule is characterized by means of gas electron diffraction (GED) with the involvement of quantum chemistry and vibrational spectroscopy. A structural analysis of the GED data is performed based on the parameters of the intramolecular potential function using of the program complex SYMM/DISP/ELDIFF/LARGE. The quadratic and cubic force constants of the urotropine molecule were obtained earlier on the basis of calculations at the MP2(full)/cc-pVTZ level and assuming molecular symmetry T _d . The values of the equilibrium geometric parameters r _e of the urotropine molecule are found. The experimental structural parameters are in good agreement with those calculated at the MP2(full)/cc-pVTZ level.