Influence of Azimuthal Structure of Surface Waves on Efficiency of their Excitation by Tubular Electron Beams

The excitation of eigen surface waves by tubular electron beams in cylindrical discharge devices is studied. The influence of the wave‐field azimuthal structure on the excitation efficiency and nonlinear stage of the plasmabeam instability is investigated both numerically and analytically. Analytical expressions for the saturation amplitude and excitation efficiency of the wave under study are derived. They are found to agree well with results obtained by numerical modelling of the plasma‐beam interaction presented in this paper. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Phase-matched four-wave mixing of isolated waveguide modes of high-intensity femtosecond pulses in a hollow photonic-crystal fiber

Hollow-core photonic-crystal fibers with a special dispersion profile are shown to allow phase-matched nonlinear optical interactions of isolated air-guided modes of high-intensity femtosecond laser pulses confined in the hollow fiber core. We present theoretical and experimental studies of the four-wave mixing of fundamental and second-harmonic pulses of a Cr:forsterite laser with an initial pulse duration of about 50 fs and an intensity on the order of 10¹⁴ W/cm² in waveguide modes of a hollow photonic-crystal fiber with a core diameter of about 13μm.     

Carbocyclic and nitrogen-containing fused CH-acids with an annelated indenyl fragment. Thermogravimetric and X-ray structural analysis of 6H-indeno[1,2-b]quinoline

Based on thermogravimetric characteristics first obtained for the model 6H-indeno [1,2-b]quinoline, the scheme of thermal conversions of this compound in the temperature range 20–700 °C has been proposed, and the limit of its thermal stability (300 °C) has been determined. This temperature is recommended as the optimum for synthesizing fused benzoaza(diaza)fluorenes. Based on the results of X-ray structural analysis, the molecules of the studied indenoquinoline form centrosymmetric pairs, which are arranged in (110) layers. The molecules are orientationally disordered. The observed self-association of these molecules is similar to the - association of fused heterocyclic systems with-excessive and ****- deficient fragments. It has been suggested that interferon-inducing and antitumor compounds with an annelated indenyl fragment have a common mechanism of action according to the intercalation model of stacking structures.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 703–709, April, 1995.     

High-resolution electron spin resonance spectroscopy of XeF* in solid argon. The hyperfine structure constants as a probe of relativistic effects in the chemical bonding properties of a heavy noble gas atom

Xenon fluoride radicals were generated by solid-state chemical reactions of mobile fluorine atoms with xenon atoms trapped in Ar matrix. Highly resolved electron spin resonance spectra of XeF* were obtained in the temperature range of 5-25 K and the anisotropic hyperfine parameters were determined for magnetic nuclei 19F, 129Xe, and 131Xe using naturally occurring and isotopically enriched xenon. Signs of parallel and perpendicular hyperfine components were established from analysis of temperature changes in the spectra and from numerical solutions of the spin Hamiltonian for two nonequivalent magnetic nuclei. Thus, the complete set of components of hyperfine- and g-factor tensors of XeF* were obtained: 19F (Aiso=435, Adip=1249 MHz) and 129Xe (Aiso=-1340, Adip=-485 MHz); g(parallel)=1.9822 and g(perpendicular)=2.0570. Comparison of the measured hyperfine parameters with those predicted by density-functional theory (DFT) calculations indicates, that relativistic DFT gives true electron spin distribution in the 2Sigma+ ground-state, whereas nonrelativistic theory underestimates dramatically the electron-nuclear contact Fermi interaction (Aiso) on the Xe atom. Analysis of the obtained magnetic-dipole interaction constants (Adip) shows that fluorine 2p and xenon 5p atomic orbitals make a major contribution to the spin density distribution in XeF*. Both relativistic and nonrelativistic calculations give close magnetic-dipole interaction constants, which are in agreement with the measured values. The other relativistic feature is considerable anisotropy of g-tensor, which results from spin-orbit interaction. The orbital contribution appears due to mixing of the ionic 2Pi states with the 2Sigma+ ground state, and the spin-orbit interaction plays a significant role in the chemical bonding of XeF*.     

Triterpene and steroid glycosides of the genusMelilotus and their genins III. Funkioside B and protodioscin from the seeds ofMelilotus tauricus

Two steroid glycosides belonging to the furostan series — funkioside B and protodioscin — have been isolated from the seeds of the plantMelilotus tauricus (Bieb.).Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 766–770, November–December, 1994.     

Reactions of photogenerated fluorine atoms with dopant molecules in solid argon

The products of UV photolysis of ternary Ar?CH₄(CD₄)?F₂ mixtures (1:c:c ₀,c, c ₀=0.001–0.01) at 13–16 K were identified by ESR and FTIR spectroscopy. These products are^?CH₃ (^?CD₃) radicals of typesI andII and molecular CH₃F?HF complexes. The latter were characterized by the IR bands of the stretching C?F (1003 cm^?1) and H?F (3774 cm^?1) vibrations. The ESR spectra of radicalsI are asymmetric. The anisotropy of theg-factor (Δg～10^?3) of radicalI indicates that the structure of the radicals is nonplanar. The ESR spectrum of the typeII radical is identical to that of matrix-isolated^?CH₃ (^?CD₃) radicals with the planar structure (Δg<5·10^?5). Under the experimental conditions, the amount of complexes formed in the photolysis is equal to 0.022·c. When the photolysis is ceased, radicalI disappears after ≈10³ s and radicalII is stabilized. The limiting concentrations of the stabilized^?CH₃ and^?CD₃ radicals are equal to 2·10^?2·c and 2·10^?3·c, respectively. A mechanism of the formation of the products is suggested. It is based on the assumption that both matrix-isolated CH₄ and F₂ and their heterodimers CH₄?F₂ are present in the samples and it takes into account the long-range migration of translationally excited flourine atoms. The CH₃F?HF complexes and radicalsI are generated by the photolysis of the CH₄?F₂ heterodimers. The decay of radicalsI is caused by geminate recombination of proximate F...CH₃ pairs. RadicalsII are formed in the reaction of translationally excited fluorine atoms with isolated CH₄ (CD₄) molecules.     

Reaction of photogenerated fluorine atoms with dopant molecules in solid argon

The products of reactions of dopant CH₄ molecules with F atoms diffusing in solid argon at 20–30 K were identified by ESR and FTIR spectroscopy. The F atoms stabilized in the matrix were generated by UV photolysis of Ar?CH₄(CD₄)?F (1000∶1∶1) samples at 13 K. Subsequent heating above 20 K results in thawing off diffusion of the F atoms and formation of products of their reaction with CH₄: radical-molecular complexes^·CH₃?HF (^·CD₃?DF) and radicals^·CH₃ (^·CD₃). The ESR spectra of the radicala are similar to those observed for matrix-isolated^·CH₃. The^·CH₃?HF complexes are characterized by the IR band of HF stetching vibration at 3764 cm^?1. Two additional splittings on the H (a _H·=2 G) and F(a _F=16G) nuclei of the HF molecule appeal in the ESR spectrum of the complex. The latter splitting is retained in the^·CD₃?DF complex, whereA _D· <0.3G The rate constant of the reaction CH₄+F→^·CH₃+HF is equal to ?10^?25 cm³s^?1 at 20 K. Its activation energy (1.7±0.2 kcal mol^?1) is ?0.5 kcal mol^?1 greater than that in the gas phase. The collinear C_3v-configuration of the^·CH₃?HF complex, which is similar to the configuration of the reagents in the transition state of the reaction considered, was established by the comparison of the exprrimental constants of hyperfine coupling with the results of the quantum-chemical calculation.