Conditions for growth of columnar and filamentary crystals

The computer model of the initial stage of condensation processes is developed. The stochastic processes of adsorption, surface diffusion, and desorption occur on the 70×70 lattice of adsorption vacancies. The model was tested by an example close to water vapor sorption on a conventional crystal surface. Computed results demonstrate the processes of nucleation, growth of crystals, and developed condensation. Computations were carried out for various adsorption energies. Results showed that with decreasing energy of adsorption the character and rate of nucleation and subsequent condensation vary. With decreasing energy of adsorption the probability of nucleation of islets on substrate reduces, the filling of the next atomic layers on islets occurs earlier than the filling of the substrate, the growth rate of islets in height increases as compared to condensation of a continuous film, and the growth rate of area of islets decreases. There is a typical energy of adsorption at which the growth rate of islets in height reaches its maximum. At a further drop of adsorption energy, there is a growth of islets only in height, the growth rate, however, reduces. The phenomena revealed in computations illustrate the mechanism of origin of columnar and filamentary crystals.     

Multifragmentation of gold nuclei by light relativistic ions: Thermal breakup versus dynamical disintegration

The multiple emission of intermediate-mass fragments (IMF) is studied for collisions of p, ⁴He, and ¹²C on Au with the 4π FASA setup. The mean multiplicities of IMF saturate at a value of around 2 for incident energies above 6 GeV. An attempt at describing the observed IMF multiplicities in the two-stage scenario, a fast cascade followed by a statistical multifragmentation, fails. Agreement with the measured IMF multiplicities is obtained by introducing an intermediate expansion phase and modifying empirically the excitation energies and masses of remnants. The angular distributions and energy spectra from p-induced collisions are in agreement with the scenario of “thermal” multifragmentation of a hot and expanded target spectator. In the case of ¹²C + Au(22.4 GeV) and ⁴He (14.6 GeV) + Au collisions, deviations from a pure thermal breakup are seen in the fragment energy spectra, which are harder than those both from model calculations and from the measured ones for p-induced collisions. This difference is attributed to a collective flow with the expansion velocity at the surface of about 0.1c (for ¹²C + Au collisions).     

Computer Simulation of the Destruction of the Organic Lanthanide Complexes under Ionizing Radiation

The calculation of defects in the structures of the Sc, La, Nd, Sm, Tb, and Yb complexes with substituted phenolate and naphtholate ligands formed under the action of neutrons with a mean energy of 2 MeV shows that the shifts of the target atoms depend on their masses and can achieve 1 μm for O, N, and S. A similar result is obtained for the calculation of the destruction of the Eu(TTA)₃(DME)₂ complex (HTTA is thenoyltrifluoroacetone). However, the treatment of the samples with the n,γ radiation does not result in destruction. Possible reasons for the found divergence between the calculated and experimental data are discussed.

     

Nonstationary formation of nanodispersed composites during vacuum deposition of a two-component vapor

A model based on the Langmuir adsorption model and a program for numerical simulation of nucleation and condensation on a cooled substrate were developed to describe the nonstationary phenomena observed in experiments on the production of nanodispersed composites by vacuum deposition of a two-component vapor. Calculations performed for a mixture of silver and water vapor have shown that the nucleation processes of the condensed phases of the components mutually stimulate each other with silver nucleation playing a leading role. A number of unusual phenomena have been found: an increase in the relative rate of water vapor condensation with a decrease in its partial pressure; the absence of stationary condensation modes; the existence of a boundary regime that separates modes with increasing and decreasing silver concentration in the condensate; the formation of porous skeletons consisting of a condensate of one of the components filled with nanoparticles of the other component. The dispersion properties of the condensates for various condensation modes and the adhesion of the condensate to the substrate were determined.     

Study of reactions of some halides, cyclopentadienyl dichlorides, and bis(cyclopentadienyl) chlorides of lanthanides withtrans-stilbene adducts with alkali metals [PhCHCHPh]·−M+ (M=Li, Na)

Reaction of Sml₂(THF)₂ with metallic lithium andtrans-stilbene in 1:2:2 ratio in DME gives the stilbene complex of divalent samarium (PhCHCHPh)Sm(DME)₂. This complex reacts with hydrogen in THF to give SmH₂(THF)₂ and 1,2-diphenylethane. The reaction with (Me₃Si)₂NH gives the amide [(Me₃Si)₂N]₂Sm(DME)₂ and the reaction with triphenylgermane yields Ph₃GeGePh₃. Reaction of CpLuCl₂(THF)₂ with 2 equivalents of [PhCHCHPh]·⁻Na⁺ in DME results in the dimerization of stilbene fragments to give anate-complex {Cp₂Lu[μ-CH (Ph)CH(Ph)CH(Ph)CH(Ph)]}Na(DME)₃. In the reaction of Cp₂GdCl with [PhCHCHPh]·⁻Na⁺, the known complex Cp₃Gd(THF) was isolated as the only lanthanidecontaining product. Published inIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1442–1446, August, 2000.     

Optimal modes for the laser cooling of solids

The method of the nonequilibrium statistical operator is employed to derive the kinetic equations for the numbers of phonons and photons and the collective population difference of the working transition that describe the laser cooling of solids. These equations are used to obtain the expressions for the efficiency of an optical heat engine in the inverse thermodynamic cycle and the limiting cooling temperature. Based on these expressions, the criteria for determining the type of the samples and the temperature and spectral ranges for the laser cooling experiments are formulated. The results of the numerical calculations are presented as supporting evidence.     

Synthesis and molecular structure of the complex YbI(bipy)(DME)2

The reaction of the naphthalene complex of ytterbium, [Yb(DME)₂]₂(μ-C₁₀H₈), with 2,2′-bipyridine in 1,2-dimethoxyethane afforded the Yb^II complex containing the 2,2′-bipyridine radical anion. The resulting complex YbI(bipy)(DME)₂ was characterized by IR and ESR spectroscopy, X-ray diffraction analysis, and magnetochemistry. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2341–2344, November, 1998.     

A chemical definition of the effective reducing power of thulium(II) diiodide by its reactions with cyclic unsaturated hydrocarbons

Thulium diiodide reduces cyclic aromatic hydrocarbons that have reduction potentials more positive than - 2.0 V versus SCE. Thus, TmI2 reacts with cyclooctatetraene or acenaphthylene in THF, or with lithium anthracenide in 1,2-dimethoxyethane (DME) to give thulium triiodide and the thulium(III) complexes [(eta8-C8H8)TmI(thf)2] (1), rac-ansa-[(eta5-C12H8)2TmI(thf)] (2), or [(eta2-C14H10)TmI-(dme)2] (3), respectively. The molecular structures of 1-3 were determined by single-crystal X-ray diffraction.     

The structure of coculine and coculidine

Conclusions It was established that the alkaloids coculine and coculidine are derivatives of D-homoindophenanthridine.This issue of the journal contains only Brief Communications.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 500–502, March, 1972.     

High current density spotless vacuum arc as a glow discharge

Vacuum discharge burning between a broad cathode and a point anode made of Mo, Cu, and Cd has been studied. This discharge operates in anode vapors and shows major arc characteristics, although no craters were examined on the cathode. The secondary electron emission is involved to explain current transport within the cathode region. This discharge is interpreted as a high density low voltage glow discharge. Having discussed the present and previous findings, the conclusion has been drawn that the secondary electron emission and “hump of potential” are dominant in the vacuum arc cathode spot