Mechanisms of spin-lattice relaxation of vk and related centers

An experimental and theoretical investigation of the spin-lattice relaxation (SLR) mechanisms of V_K-centers in alkali and alkaline earth halides has been carried out. It has been shown that at low temperatures the main role in SLR is played by rapidly relaxing centers (RRC). In some cases, however, an intrinsic one-phonon SLR process due to modulation of both the isotropic and anisotropic hyperfine (HF) interaction seems to be important. At higher temperatures SLR can be explained by an anharmonic Raman process with the participation of the resonant molecular vibrational (RMV) mode of the V_K-center. In this SLR process, similarly to the low-temperature intrinsic process, the spin-phonon coupling is due to the modulation of the HF interaction. Deviations from the Debye phonon spectrum and the local anharmonicity of V_K-centers turn out to be important. The SLR of several other hole and interstitial type centers in alkali halides has also been investigated and their SLR mechanisms are discussed.     

Solution of an axisymmetric problem of thermoelasticity by the method of component-by-component decomposition

Zaporozh'ye Institute of Mechanical Engineering. Translated from Prikladnaya Mekhanika, Vol. 27, No. 1, pp. 31–40, January, 1991.     

EPR spectrum of donors in 6H SiC in a broad temperature range

An EPR study of donors in 6H SiC crystals with an uncompensated donor concentration (N _D−N _A) of 2×10¹⁸ to 1×10¹⁶ cm⁻³ performed in the temperature range 4.2 to 160 K at frequencies of 9 and 140 GHz showed that 6H n-SiC samples have two donor states in the gap. One of them originates from nitrogen occupying three inequivalent lattice sites with ionization energies of 150 and 80 meV, and the second is connected with a structural defect lying deeper in the gap than nitrogen. The temperature dependences of donor EPR line intensities have been found to deviate from the Curie law. The observed EPR line-intensity peaks of donors are produced in a temperature-driven successive redistribution of donor electrons between the donor levels. The temperature dependences of EPR line intensities obtained from samples with low donor concentrations were used to determine the valley-orbit splitting of nitrogen in cubic sites. Fiz. Tverd. Tela (St. Petersburg) 40, 1824–1828 (October 1998)     

Analysis of the Properties of Carbon Nanotubes from Distribution Maps of Molecular Electrostatic Potential

The electronic structure and stereochemical structure of some types of carbon nanotubes were investigated by quantum-chemical methods. It was found that the "zigzag" configurations have significant dipole moments and are characterized by dimorphism, reflected in the existence of symmetrical and unsymmetrical states.     

Solution of three-dimensional static problems of thermoelasticity

Zaporozh Institute of Mechanical Engineering. Translated from Prikladnaya Mekhanika, Vol. 30, No. 3, pp. 25–34, March, 1994.     

Change in the IR spectra and nature of the thermal transformations of products of chemisorption of amino acids on a dehydrated silica surface

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 55, No. 3, pp. 405–409, September, 1991.     

Behavior of serine proteases thrombin,trypsin, and chymotrypsin under conditions of MALDI-TOF-Mass spectrometry

Features of ion formation under the influence of laser emission under the conditions of MALDI-TOF mass spectrometry in the glycosylated protein thrombin and the related proteases trypsin and chymotrypsin were studied for the first time. It was shown that trypsin and chymotrypsin are ionized in the form of molecular ions with masses 23800 and 25660 Da respectively. The molecular ion of thrombin was not detected; three main fragment ions with masses 9951, 10230, and 11982 Da were detected in the mass spectrum of thrombin. It was suggested that these fragments relate to peptide and glycopeptides fragment ions formed as a result of bond cleavage in the region of Asn60G during exposure to laser emission under the conditions of MALDI-TOF mass spectrometry. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 44, No. 2, pp. 74–78, March–April, 2008.     

Spin-lattice relaxation of the Vk-center in LiF

The angular and temperature dependences of the spin-lattice relaxation (SLR) rate of V_k-centers in LiF doped with Mg or Ag have been investigated. In the temperature interval 4.2–100 K the results can be fitted by the formula $\text{τ}{}^{\mathrm{?1}}\text{= A(θ)T + Be}{}^{\mathrm{<mtext>?\Delta </mtext><mtext>T</mtext>}}$ with A(0°) = 0.11 sec^?1K^?1, A(90°) = 1.3 sec^?1K^?1, B = 3 × 10⁵sec^?1 and Δ = (175 ± 15)K.A mechanism for the SLR is considered, assuming the modulation of the hyperfine interaction by phononinduced transitions between the ground and excited states of the resonant molecular vibrations of the V_k-center. This mechanism is found to explain the value, the temperature dependence and the isotropy of τ^?1 in the interval T = 20–100 K.The one-phonon SLR mechanisms of the V_k-center in the T < 10 K region are discussed.     

Effect of the target on the efficiency of generation of monomolecular ions of fluorine-containing amino acids in laser desorption/ionization

A comparative analysis was carried out on the laser desorption/ionization (LDI) mass spectra of fluorine derivatives of N-phenylphenylglycine using different targets. The extent of generation of molecular ions of the fluorine-containing amino acids was shown to depend significantly on the nature of the target surface. Alkali metal chlorides (LiCl, NaCl, KCl, and CsCl) have the highest efficiency among the targets studied (standard metal target, polished monocrystalline silicon, glass, silica) in the generation of molecular ions of fluorine-containing amino acids, which increases in the series LiCl < NaCl < KCl < CsCl. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 45, No. 3, pp. 167-172, May-June, 2009.