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  • 1
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 9401-9411 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Time dependent Monte Carlo (TDMC) simulations are performed to determine the effects of a variety of H reactions at a diamond {001}(2×1) surface exposed to gaseous atomic and molecular hydrogen under chemical vapor deposition conditions. The simulation time in the TDMC method is the same as the real time measured in experiments because all of the considered reactions are allowed to occur with probabilities which are the product of the TDMC time step and the corresponding reaction rates. The reaction rates are either explicitly calculated via molecular dynamics or transition state theory methods, or taken from experimental measurements. The simulation takes into account H adsorption, H abstraction, H2 desorption, H diffusion, and the reverse of these reactions. The relative values of the calculated rates and how they affect the surface radical density and distribution, as well as the effect of CH3 on radical site diffusion are discussed. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 5997-6008 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Time dependent Monte Carlo (TDMC) simulations are performed on a diamond lattice to determine the effect of surface properties/conditions on the growth of diamond thin films on flat and stepped diamond {001}(2×1):H surfaces under chemical vapor deposition conditions. The gas–surface interface consists of reactions of incoming gas-phase species, such as H2 molecules and H and CH3 radicals with surface radical, π-bond and step edge sites on the diamond {001}(2×1):H surface. The rates and probabilities of adsorption, abstraction, desorption, and incorporation reactions, as well as the reverse reactions, are explicitly calculated either via molecular dynamics or transition state theory methods, or taken from experimental measurements. The TDMC method allows all these reactions to occur simultaneously, though probabilistically, at each time step. The microscopic and macroscopic characteristics of the growing film are observed as functions of time. Diamond films of 10∼100 layers are grown in the simulation and the observed growth rate (∼0.5μm/h at 1200 K) is in agreement with experimental results. The contributions to the activation energy of growth by specific processes such as H abstraction, CH3 adsorption and CH2 incorporation into the trough sites have been determined. The contributions to the activation energies by specific processes are not linearly additive, and the CH3 adsorption at step edges leads to enhanced growth at the edges. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 31 (1991), S. 596-606 
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Optimal jacket-fluid temperature profiles for tubular Nylon 6 reactors (in the presence of radial gradients of temperature and concentration) have been obtained using an algorithm based on the continuous minimum principle developed for a distributed parameter system. A gradient search technique has been devised and implemented for obtaining these optimal profiles. The optimal temperature profiles are found to be at the maximum permissible temperature, Tmax, at the beginning of the reactor and then slowly decrease to the minimum permissible temperature, Tmin, near the end of the reactor. The effect of varying several parameters is also studied. The desired value of the chain length and the reaction time are found to be the parameters which effect the optimal profiles most significantly.
    Zusätzliches Material: 12 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 4
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 27 (1989), S. 616-623 
    ISSN: 0749-1581
    Schlagwort(e): 13NMR ; Tertiary arsine ; Aminoarsonium ions ; Arsonium ions ; Aminoarsines ; 1H NMR ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: 13C and 1H NMR spectral data for a homologous series of tertiary arsines (R3As, where R = Me, Et, n-Pr and Ph), aminoarsines and arsonium and aminoarsonium salts are reported and discussed. In nearly all cases, quaternization of the tertiary arsine to its corresponding arsonium or aminoarsonium salt causes a decrease in the magnitude of δc. These results are compared with those from an analogous study on the quaternization of tertiary phosphines, R3P. A discussion of the factors that affect the relative magnitudes of δc and R3As and R3P is given. Hammett-Taft dual substituent parameter analysis was used to show that the positive charge on the arsenic in the atomatic quaternary salts is delocalized by an inductive mechanism. The 1H NMR spectra of the n-propyl- and phenyl-containing compounds are non-first order. The δH and nJ(HH) values were determined by iterative computer analysis. Likewise, the nJ(CH) values for the phenyl carbons of [Ph3AsNH2]Cl and [Ph3AsNHMe]Cl were determined from the coupled 13C NMR spectra.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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