A mass spectrometric study of the vaporization of erbium hexafluoroacetylacetonate

The sublimation of erbium tris-hexafluoroacetylacetonate Er(C₅O₂HF₆)₃ was studied by the Knudsen effusion method with the mass spectrometric determination of vapor composition. Groups of ions containing one, two, and three metal atoms were recorded. The enthalpies of sublimation of the monomeric, dimeric, and trimeric forms Δ_S H°(362 K) were found to be 133 ± 4, 135 ± 7, and 139 ± 38 kJ/mol, respectively. The melting point of Er(C₅O₂HF₆)₃ was 390 ± 2 K. No oligomeric forms were observed in vapor superheated above 430 K.     

Possible explanation of the difference in nuclear fission induced by the intermediate energy protons and neutrons

A possible explanation is given of the experimentally observed differences between the the fission cross-sections in the reactions induced by the intermediate energy (hundreds MeV) neutrons and protons. Received: 13 June 2000 / Accepted: 6 July 2000     

On the fundamental homology classes of a real algebraic variety

It is proved that there is only one relation between the homology classes determined by the real points of a special real algebraic variety. This relation is equal to the sum of all the homology classes. Translated fromMatematicheskie Zametki, Vol. 66, No. 2, pp. 216–219, August, 1999.     

Electron diffraction and quantum chemical study of the molecular structure of 4-methylbenzene sulfochloride

A combined electron diffraction and mass spectrometric study was carried out to investigate the molecular structure of 4-methylbenzene sulfochloride at 330(2) K. An analysis of the electron diffraction data was performed in terms of the r_α structure. Several models of geometrical structure having different orientations of the sulfochloride group relative to the plane of the benzene ring are treated. The following values of structural parameters were obtained: r_α(C-H)_meth= 1.104(41)Å, r_a(C-H)/_phen = 1.103(27)Å, r_a(C-C)_phen = 1.403(7) Å, r_a(C-C)_meth = 1.512(25) Å, r_a(C-S) =1.758(6) Å, r_a(S = O) = 1.419(3) Å,r _a(S-Cl) = 2.049(5) Å, ∠CCH_meth = 106.9(47)?, ∠CSO = 110.5(6)?, ∠CSCl = 101.3(6)°, ∠OSO = 120.5(9)°. The angle between the plane of the benzene ring and the plane of the S-Cl bond was found to be 83°. Ab initio and semiempirical quantum chemical calculations were accomplished to estimate the geometrical and energy parameters and compare them with electron diffraction data.     

All-optical confinement of ultracold plasma with resonant ions

The solution of the problem of all-optical (nonmagnetic) confinement of ultracold electron-ion neutral plasma based on selective action on plasma ions with quantum transition J=1→J=0 of so-called rectified radiation forces in a strong nonmonochromatic light field is suggested. The presented scheme of the three-dimensional dissipative optical trap for plasma allows one to obtain long-lived ultracold plasma with controlled characteristics. The lifetime of the ultracold plasma in such a trap may exceed considerably (by orders of magnitude) the time of free plasma expansion and the lifetime in the (earlier proposed) optical molasses for the ultracold plasma.     

Dynamics of redox processes and electrochromism of films of zirconium (IV) phthalocyanines with out-of-plane β-dicarbonyl ligands

The electrochromic properties of the mixed-ligand zirconium phthalocyanine complex films have been investigated. Voltammetric characteristics, absorption spectra of films as a function of potential, and curves of current and absorption at the Q-band maximum in the case of their reversible oxidation in 1 N KCl against time have been measured. An analysis of the time-current dependence allowed us to find that the dynamics of the reversible oxidation of phthalocyanine complexes in such films are determined by the codiffusion in their bulk of positive and negative carriers (as Cl^? anions) with effective diffusion coefficient D_eff = ~ 10^? 13 cm²/s. The same value of D_eff has been obtained from measurements of the curve of optical density in the region of the Q-band maximum against time.     

Topological classification of real three-dimensional cubics

Mathematical Notes - The paper is devoted to finding topological types of nonsingular real three-dimensional cubics. It is proved that the following topological types exist: the projective space,...     

Electret processes in disordered systems based on liquid dispersion media

Electret-thermal analysis (ETA) of disordered systems based on dispersed media is carried out. It is shown that the method of thermally stimulated currents makes it possible to estimate the structural changes occurring in a liquid dispersion medium. It is found that liquid water in a free state exhibits the electret properties. The observed multiple peaks on the thermally stimulated current curve are the evidence of the multicomponent nature of the ??free water?? system. The mechanisms of processes leading to the formation of the electret state in such systems are considered.     

Light Absorption by the Clusters of Colloidal Gold and Silver Particles Formed During Slow and Fast Aggregation

Spectra of absorption (400–800 nm) by the aggregates of colloidal gold (5, 15, and 30 nm in diameter) and silver (20 nm in diameter) particles were studied experimentally and theoretically. It was revealed that, during fast aggregation corresponding to the diffusion-limited cluster aggregation (DLCA), the pattern of spectra is dependent on the size of primary particles. Spectra with the additional absorption maximum in the red region are observed for 15 and 30 nm gold and 20 nm silver particles, while the absorption spectrum for 5 nm particles is characterized by only one maximum shifted to the red region. The slow aggregation resulted in a decrease in plasmon absorption peak with no marked shift to the red region and to the broadening of long-wave absorption wing. From data on electron microscopy, typical branched DLCA-clusters were formed during fast aggregation, whereas small compact aggregates and a noticeable number of single particles were observed in a system during slow aggregation. The computer model of the diffusion-limited cluster-cluster aggregation was used to explain these results. Optical properties of aggregates were calculated using coupled dipole method (CDM or DDA) and the exact method of a multipole expansion. Corrections for the size effect were introduced into the bulk optical constants of metals for nanosized particles. It was shown that a modified version of DDA (Markel et al.,Phys. Rev. B, 1996, vol. 53, no. 5, p. 2425) allows us to explain the pattern of experimental spectra of DLCA-aggregates and their dependence on a monomer size. The exact method was applied to calculate the extinction cross sections of metallic aggregates demonstrating strong electrodynamic interaction between particles. The number of higher multipoles that are required to adequately describe this interaction is much larger than the number of terms of an ordinary Mie series and is the main obstacle to the exact calculation of the spectra of metallic aggregates with a large number of particles.     

On the picard group and the brauer group of a real algebraic surface

The map of the Brauer group of a real algebraic surface to the invariant part of the Brauer group of its complexification is studied. In this study, the real cycle map of the Picard group is used. Translated fromMatematicheskie Zametki, Vol. 67, No. 2, pp. 211–220, February, 2000.