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  • Articles  (484)
  • 1995-1999  (347)
  • 1960-1964  (137)
  • Chemistry and Pharmacology  (484)
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  • Articles  (484)
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  • 1
    Electronic Resource
    Electronic Resource
    A new He–CO interaction energy surface with vibrational coordinate dependence. II. The vibrational deactivation of CO(v=1) by inelastic collisions with 3He and 4He (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 9929-9934 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Vibrational relaxation cross-sections and rate constants have been calculated for the deactivation of CO(v=1) by 3He and 4He on a new intermolecular potential with vibrational coordinate dependence [T. G. A. Heijmen, R. Moszynski, P. E. S. Wormer and Ad van der Avoird, J. Chem. Phys. 107, 9921 (1997)]. The new surface is found to resolve the qualitative discrepancy between theory and experiment which existed in earlier theoretical calculations. The low impact energy regime has also been investigated focussing in particular on impact energies of less than 15 cm−1 above the vibrational (v=1) threshold. Resonance structure has been found to occur and a comparison is made with an earlier investigation of the low temperature region. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.475295
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  • 2
    Electronic Resource
    Electronic Resource
    Dissociative electron attachment in nanoscale ice films: Temperature and morphology effects (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 8668-8677 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The electron-stimulated desorption (ESD) of D− ions from condensed D2O films is investigated. Three low-energy peaks are observed which are identified as arising from excitation of 2B1, 2A1, and 2B2 dissociative electron attachment (DEA) resonances. A fourth, higher energy feature is also seen in the D− yield which is likely due to the formation of a transient anion state that dissociates and/or decays into a dissociative excited state. The energies and ion yields of the resonances vary with the temperature and morphology of the D2O film. Below 60 K, the work function of the ice films changes with temperature and the DEA resonances shift in energy. The D− ESD yield generally increases with temperature, but it deviates from this trend at temperatures corresponding to structural phase transitions in ice. The (2B1) D− temperature dependence is remarkably similar to that observed for the ESD of low-energy D+ ions from D2O ice, even though the two originate from different electronic excitations. These results are attributed to thermally induced changes in the hydrogen bonding network, which changes the lifetimes of the predissociative states that lead to ESD and which also allows for the reorientation of surface molecules. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.475019
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  • 3
    Electronic Resource
    Electronic Resource
    Scattering-angle resolved product rotational alignment for the reaction of Cl with vibrationally excited methane (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 5961-5971 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have applied the experimental technique of core extraction [W. R. Simpson et al., J. Chem. Phys. 103, 7299 (1995)] combined with resonance-enhanced multiphoton ionization (REMPI) with a polarized laser beam to probe the angular-momentum alignment of the HCl product of the reaction of Cl with vibrationally excited CH4(ν3=1). The core extraction method permits us to distinguish products scattered in different directions in the center-of-mass frame, and thus we are able to determine the rotational alignment for various product scattering angles for individual HCl(v,J) quantum states (a state-resolved three-vector correlation). For the forward-scattered HCl(v=1, J=1) we observe a large positive rotational alignment. This positive velocity-angular-momentum correlation is interpreted to be the result of the angular momentum of the HCl product being directed in the plane perpendicular to the line-of-centers force in a simple hard-sphere scattering model. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.473262
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  • 4
    Electronic Resource
    Electronic Resource
    Dissociative electron attachment in nanoscale ice films: Thickness and charge trapping effects (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 5027-5034 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The yield and kinetic energy (KE) distributions of D− ions produced via dissociative electron attachment (DEA) resonances in nanoscale D2O ice films are collected as a function of film thickness. The 2B1, 2A1, and 2B2 DEA resonances shift to higher energies and their D− ion yields first increase and then decrease as the D2O films thicken. The D− KE distributions also shift to higher energy with increasing film thickness. We interpret the changes in the DEA yield and the D− KE distributions in terms of modifications in the electronic and geometric structure of the surface of the film as it thickens. A small amount of charge build-up occurs following prolonged electron beam exposure at certain energies, which primarily affects the D− KE distributions. Charge trapping measurements indicate that an enhancement in the trapping cross section occurs at energies near zero and between 6 and 10 eV. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.475924
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  • 5
    Electronic Resource
    Electronic Resource
    Vibrational energy transfer between the isotopomers of carbon monoxide at low temperatures (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 485-491 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Rate constants have been measured for vibration to vibration energy transfer from 12C16O(v=1) to the first vibrationally excited state of both 13C16O (Δν¯=47 cm−1) and 13C18O (Δν¯=100 cm−1) using the infrared laser fluorescence technique over the temperature range 50 to 270 K in the gas phase and in liquid neon, deuterium and argon solutions. Fluorescence from 12C16O(v=1) was filtered out, and the time-dependence of the fluorescence intensity from the other isotopomer used to determine the rate constants for energy transfer. The results for the two isotopomeric systems are markedly different. For that with the smaller energy mismatch, 12C16O–13C16O, the rate constants increase with decrease in temperature from 270 to 80 K. This is shown to be consistent with near-resonant energy transfer mediated by transition dipole-transition dipole couplings. Below 80 K, the temperature dependence of the rate constants flattens. For the 12C16O–13C18O system, the rate constants decrease with decrease in temperature from 270 to 100 K, below which they increase with further decrease in temperature. The temperature dependence in the range 270 to 100 K is shown to be consistent with energy transfer mediated by a combination of by long range and short range forces. Below 100 K, the temperature dependence of the rate constants is governed by attractive forces which influence the collision pair during their encounter. The rate constants are compared with previous studies of near-resonant vibrational energy transfer in other systems at low temperatures. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.475411
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  • 6
    Electronic Resource
    Electronic Resource
    The vibrational deactivation of CO(v=1) by inelastic collisions with H2 and D2 (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 4931-4944 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Calculations of the relaxation rate constants, kCO–H2, for the vibrational deactivation of CO(v=1) by pH2 and oH2 are reported in the temperature range 30 K〈T〈300 K. The CO rotation is treated using the infinite-order sudden (IOS) approximation, while the rotation of H2 is included using the coupled states (CS) approximation. A near-resonant energy transfer process, in which the H2 molecule is rotationally excited from J=2 to J=6 on relaxation of CO(v=1), is found to account for the experimental observation that kCO–pH2/kCO–oH2〉1 for this system at temperatures above 80 K. Evidence is presented to suggest that below this temperature, which represents the current lower limit of existing experimental data for the CO(v=1)-pH2 system, thermal depopulation of the J=2 rotational state in pH2 reduces the importance of the near-resonant energy transfer process in the determination of kCO–pH2. For T(very-much-less-than)80 K the ratio kCO–pH2/kCO–oH2〈1 is predicted on the basis of these calculations. At impact energies less than 60 cm−1, the relaxation cross sections increase at a rate which is insufficient to account for the observed upturn in the experimentally determined deactivation rate constants for the CO–nH2 system below 60 K. Rate constants for the deactivation of CO(v=1) by oD2 and pD2 have also been calculated and compared with experimental data. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.473542
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  • 7
    Electronic Resource
    Electronic Resource
    Vibrational energy transfer between isotopes of CO and isotopes of CO2 in the gas phase and in liquid Kr solution (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 1192-1198 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Rate constants are presented for (VV) energy transfer between CO(ν=1) and CO2(0001) in the gas phase down to 115 K and in liquid Kr solution at 118 and 130 K. Four isotopically substituted systems were investigated for which the energy mismatches varied between 104 and 306 cm−1. The gas and liquid phase data show several systematic effects with changing energy mismatch. In particular it was found that the ratio of the liquid and gas phase rate constants at the same temperature, kL/kG, increased with decreasing energy mismatch. This is not predicted by current theories of liquid phase energy transfer and is in contrast to previous work using liquid Kr as the solvent. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468906
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  • 8
    Electronic Resource
    Electronic Resource
    Vibrational relaxation of CO (v=1) by inelastic collisions with 3He and 4He (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 2528-2537 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Calculations of the vibrational relaxation rate constants of the CO–3He and CO–4He systems are extended to lower temperatures than in any previous calculation and a comparison made with new experimental results in the temperature range 35–295 K for CO–3He and previously published results in the range 35–2300 K for CO–4He. Both the coupled states (CS) and infinite-order sudden (IOS) approximations are used, with the self-consistent-field configuration interaction CO–He interaction potential of Diercksen and co-workers. The CS approximation is found to give a similar level of agreement with experiment for the two isotopic species, while the performance of the IOS approximation is system dependent. The discrepancy between experimental and theoretical IOS rate constants is quite different for collisions involving 3He and 4He, so that it is not profitable to compare IOS results directly with experiment for these two systems at temperatures below 300 K. The differences between the measured and the CS calculated rate constants for both the CO–4He and CO–3He systems are thought to be due predominantly to inaccuracies in the interaction potential. Relaxation rate constants for CO target molecules in collision with HD, D2 and H2 are compared with results involving 3He, 4He, and "2He,'' revealing some systematic trends depending only on mass. However, for all hydrogen species there are marked upturns in the rate constants at low temperatures relative to those for helium atoms, while the rate constants for HD are greater than those for 3He throughout the temperature range. Calculations at small initial kinetic energies for the CO–He systems reveal an unexpected increase in relaxation cross section with reduction in kinetic energy. This implies that at very low temperatures the CO–He rate constants will show an upturn with decreasing temperature. The fact that this effect is smaller than that for the CO-hydrogen systems and occurs at lower temperatures is consistent with the shallower CO–He attractive well compared with that for CO–H2. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469674
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  • 9
    Electronic Resource
    Electronic Resource
    The temperature dependence of the Cl2/GaAs(110) surface product distribution (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 320-325 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The reaction of Cl2 with GaAs(110) is studied with soft x-ray photoelectron spectroscopy (SXPS). The temperature dependence of the surface product distribution, in the range of 300–650 K, is derived from SXPS core-level and valence-band spectra and compared to known gas-phase product distributions. It is found that both Ga and As chlorides are formed at room temperature. Following reaction at temperatures above ∼400 K, no Cl remains on the surface. Instead, for temperatures up to ∼600 K an As overlayer is formed, whereas reaction at ∼650 K leads to the stoichiometric removal of Ga and As. These findings indicate that there is a direct correlation between the surface and gas-phase product distributions. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470903
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  • 10
    Electronic Resource
    Electronic Resource
    Incorporation of Imidazolium Cations into an Enantiomeric Tartrate Host Lattice: Designing New Nonlinear Optical Materials (1995)
    s.l. : American Chemical Society
    Chemistry of materials 7 (1995), S. 909-919 
    Details
    ISSN: 1520-5002
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/cm00053a016
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