Potential energy surface and orientational disorder in solid fullerene C60

The polymorphism and molecular disorder in crystalline C₆₀ have been studied by modelling the optimum packing of fullerene molecules by the atom-atomic potential method. The study includes the calculation of minima and saddle points of the potential energy surface with sorting out of the most common space symmetry groups. Two models of intermolecular potential for C₆₀ have been checked, one of which assumes effective charges at the centers of C-C bonds. It has been found that the calculated barrier of reorientations is much lower in the case where the concerted character of rotations of different molecules is taken into account. The model of orientational disorder in the face-centered cubic phase is suggested, which is based on consideration of symmetrically arranged equivalent minima separated by low potential barriers.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1466–1469, August, 1995.The work was financially supported by the Russian Foundation for Basic Research (Project No. 94-03-08895).     

Stereochemistry of the asymmetric 1,4-hydride reduction of N-substituted derivatives of δ9,10-octahydro-4-quinolone

It is shown that the reaction of LiAlH₄ with ^{9, 10}-ocathydro-4-quinolones that have chiral (S)-sec-butyl and (S)--benzylethyl substituants at the nitrogen atom proceeds as asymmetric 1,4-hydride reduction with the primary formation of trans isomers of (1S)-sec-butyl(9S,10S)- and (1S)--benzylethyl(9S,10S)-decahydro-4-quinolones, the three-dimensional structures and absolute configurations of which were established by ¹³C NMR spectroscopy and circular dichroism measurements.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 519–523, April, 1983.     

Detailed kinetic modeling of soot formation in shock tube pyrolysis and oxidation of toluene and n-heptane

A new detailed kinetic model of soot formation in shock tube pyrolysis and oxidation of aliphatic and aromatic hydrocarbons is proposed. The model is based on the comprehensive kinetic model of PAH formation and growth [H. Richter, J.B. Howard, Phys. Chem. Chem. Phys. 4 (2002) 2038-2055; H. Richter, S. Granata, W.H. Green, J.B. Howard, Proc. Combust. Inst. 30 (2005) 1397-1405; J. Appel, H. Bockhorn, M. Frenklach, Combust. Flame 121 (2000) 122-136; M. Frenklach, D.W. Clary, T. Yuan, W.C. Gardiner, Jr., S.E. Stein, Combust. Sci. Tech. 50 (1986) 79-115; M. Frenklach, J. Warnatz, Combust. Sci. Tech. 51 (1987) 265-283; M.S. Skjøth-Rasmussen, P. Glarborg, M. Østberg, J.T. Johannessen, H. Livbjerg, A.D. Jensen, T.S. Christensen, Combust. Flame 136 (2004) 91-128], on the new concepts of soot particle nucleation [A. Violi, Combust. Flame 139 (2004) 279-287; A. Violi, A.F. Sarofim, G.A. Voth, Combust. Sci. Tech. 176 (2004) 991-1005; A. D’Alessio, A. D’Anna, P. Minutolo, L.A. Sgro, A. Violi, Proc. Combust. Inst. 28 (2000) 2547-2554; A. D’Anna, A. Violi, A.D’Alessio, A.F. Sarofim, Combust. Flame 127 (2001) 1995-2003] and the traditional H-abstraction/C₂H₂-addition (HACA) route of PAH and soot particles surface growth [H. Wang, M. Frenklach, Combust. Flame 110 (1997) 173-221; J. Appel, H. Bockhorn, M. Frenklach, Combust. Flame 121 (2000) 122-136]. The gas-phase kinetic scheme was validated against the experimentally measured concentration profiles of the main gas-phase species formed during toluene pyrolysis and H and OH radicals during benzene and phenol pyrolysis and toluene oxidation behind reflected shock waves. The model describes the main characteristics of soot formation in pyrolysis and oxidation of toluene and n-heptane oxidation under conditions typical of shock tube experiments. Both hydrocarbons have the same number of carbon atoms but different structures, which causes different behavior of the systems. The discrete Galerkin technique was applied for direct counting of the mean number of active sites formed on the surface of soot precursors and soot particles in reactions of activation, deactivation, and surface growth.     

Absolute calibration of photodetectors: photocurrent multiplication versus photocurrent subtraction

We report testing of the new absolute method of photodetector calibration based on the difference-signal measurement for two-mode squeezed vacuum by comparison with the traditional absolute method based on coincidence counting. Using low-gain parametric downconversion, we have measured the quantum efficiency of a counting detector by both methods. The difference-signal method was adapted for the counting detectors by taking into account the dead-time effect.     

Reaction mechanism of CO methanation on nickel catalysts,as studied by isotopic and nonstationary methods

Kinetic isotope effects were measured upon the replacement of hydrogen by deuterium in the reaction of carbon monoxide methanation on nickel catalysts supported on TiO₂ and γ-Al₂O₃. Data on the mechanism of the process were obtained with the use of a nonstationary method. A step-scheme was proposed, in which the interaction of oxygen-containing compounds with hydrogen is a slow step of the process.     

How confinement affects the dynamics of c60 in carbon nanopeapods

The dynamics of confined systems is of major concern for both fundamental physics and applications. In this Letter, the dynamics of C60 fullerene molecules inside single walled carbon nanotubes is studied using inelastic neutron scattering. We identify the C60 vibrations and highlight their sensitivity to temperature. Moreover, a clear signature of rotational diffusion of the C60 is evidenced, which persists at lower temperature than in 3D bulk C60. It is discussed in terms of confinement and of reduced dimensionality of the C60 chain.     

Inelastic magnetic neutron scattering from inner filled shells of impurity atoms in metals

The differential cross section of inelastic magnetic neutron scattering by paired electrons of inner filled s ² shells of impurity atoms in metals is first derived taking into account single electron excitations from the inner shell of the impurity to the free states of the metal. The energy-angle distributions of the scattered neutrons are calculated depending on the effective electronic mass near the Fermi surface.