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  • 1
    Electronic Resource
    Electronic Resource
    Dissociative attachment reactions in electron stimulated desorption from condensed O2 and O2-doped rare-gas matrices (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 2664-2674 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Desorption of the ions O−, O−2,O−3 (and/or O2⋅O−) induced by electron impact on pure O2 multilayer films and Ar, Kr, and Xe matrix films containing O2 is reported. In addition to these anions, the ionic complexes M⋅O− (M=Ar and Kr) are also observed to desorb from Ar and Kr matrices, respectively. In the range 4–16 eV, the incident electron energy (Ei) dependence of the yields (i.e., the yield functions) of all the diatomic and triatomic anions exhibit features which can be correlated with the O− yield function; indicating that, these anions are produced by dissociative attachment reactions whose first step involves the formation of O−2 quasibound states. From analysis of all yield functions and variations of the anion yields as a function of O2 concentration in the matrices, we find that the simplest dissociative transient state, which can propel in vacuum an M⋅O− or O2⋅O− ion, must have the configuration M⋅O2⋅O−*2. To explain the formation of O−2 and O−3 ions below Ei(approximately-equal-to)6 eV, the existence of an electronically excited O−4 state decaying into the limits O−2+O2 and O−3+O must be postulated. At higher energies, O−2 can be formed by the reaction of O− (produced by dissociating O−2 states) with other O2 molecules (e.g., O−+O2→O−3→O−2+O). Both transient anion, M⋅O2O−*2,O−*4 result from initial electron capture by an O2 molecule in a dimeric configuration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456976
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  • 2
    Electronic Resource
    Electronic Resource
    Surface reactions between O2 and hydrocarbons induced by dissociative electron attachment (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 7476-7482 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Desorption of O− and OH− ions induced by low-energy (4–20 eV) electron impact on O2 and hydrocarbon molecules (CnH2n+2, n=5 and 8; CnH2n, n=2, 3, and 4) coadsorbed on Pt is reported. The magnitude of the O− and OH− signals is investigated as a function of incident electron energy and substrate coverage. Beyond monolayer coverage, results are provided for two types of coadsorption: a single hydrocarbon layer physisorbed on a multilayer O2 film and a multilayer film containing 25% volume O2 mixed with hydrocarbon molecules. For all experiments, the OH− yield function can be correlated with that of the O− signal from pure O2 and hydrocarbon–O2 mixture films. This result indicates that the OH− ions are produced by the abstraction reactions O−+CnH2n+2→OH−+CnH2n+1 and O−+CnH2n→OH−+CnH2n−1 where O− ions are generated by the dissociative attachment reaction e+O2 (3∑−g)→O−2 (2∏u,2∑+g,2∑+u)→O− (2P)+O(3P,1D). The observed reaction efficiency for OH− formation, defined as the ratio of the OH− intensity to that of O−, is found to increase with coverage of the substrate by C4H8–O2 and C5H12–O2 mixtures. It reaches values of 3% and 8%, respectively, above 3 monolayers for incident electrons of 13 eV. The energetics involved in those reactions as well as the behavior of the OH− intensity as a function of incident electron energy and coverage strongly suggest that OH− arises from dissociation of the intermediate quasi-bound anions CnH2n+2 O− and CnH2n O− into the limits OH−+CnH2n±1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459422
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  • 3
    Electronic Resource
    Electronic Resource
    Mechanisms for O− electron stimulated desorption via dissociative attachment in condensed CO (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 5166-5170 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The formation of O− ions via dissociative attachment (DA) in electron stimulated desorption from condensed CO is reported. The 2Π states of CO− previously observed in the gas phase and CO− states with the forbidden symmetry Σ− are involved below and above 13 eV, respectively, in the DA processes. Measurements of the kinetic energy of O− ions indicate that they suffer post dissociation interactions with the neighboring CO molecules before leaving the solid.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454671
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  • 4
    Electronic Resource
    Electronic Resource
    Electron stimulated desorption via dissociative attachment in amorphous H2O (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 8570-8576 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Low energy (0–12 eV) electron impact on condensed amorphous H2O and D2O films is shown to induce electron stimulated desorption of H− and D−, respectively, via dissociative electron attachment. The onsets for H− and D− detection are at 5.5 eV, with a maximum yield for anion desorption at ∼7.4 eV. The kinetic energy distributions of the desorbing anions are peaked near 0 eV, indicating that the anions suffer post-dissociation collisions at or near the surface, with a large probability of anion trapping on the surface. The present results provide direct information on the dissociation products, prior to the interferences of subsequent reaction processes in the condensed film.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460090
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  • 5
    Electronic Resource
    Electronic Resource
    Production of anion–atom complexes by electron stimulated desorption (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 3402-3403 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report the formation of the anion–atom complexes ArO− and ArCl− by electron stimulated desorption from multilayer argon films containing O2, N2O, and Cl2 molecules.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455845
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  • 6
    Electronic Resource
    Electronic Resource
    Dynamics of dissociative attachment reactions in electron stimulated desorption: Cl− from condensed Cl2 (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 2292-2296 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Energy analysis of Cl− ions produced by dissociative attachment in electron stimulated desorption from Cl2 condensed on a platinum substrate is reported. The electron energy dependence of the Cl− signal exhibits two peaks around 2 and 5 eV which arise, respectively, from the 2Πg and 2Πu core-excited Cl−@B|2 resonant states. At higher Cl2 coverages, a third peak is observed around 11.5 eV. From kinetic energy distributions, it is possible to ascribe this latter peak to Cl− ions formed via the 2Πu resonance by electrons which have suffered energy losses through the excitation of low-lying electronic states of molecular chlorine. In the energy range of the 2Πu Cl−*2 resonance, we observe that multiple scattering processes are also important and that the curve representing the kinetic energy of Cl− ions formed via a single scattering process as a function of incident electron energy is a straight line with a slope 1/2. This indicates that the chlorine lattice is not involved in the dissociation dynamics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453160
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  • 7
    Electronic Resource
    Electronic Resource
    Stabilization of transient negative ions by vibrational energy transfer: A cluster and thin film study on SF6 and C6F6 (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 9046-9051 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Resonant low energy electron attachment to SF6 and C6F6 in argon clusters and on a multilayer krypton film is presented. The energy dependence of the absolute attachment cross sections for the condensed molecules is determined in the range 0–8 eV by measuring charge localization on the film. We find a cross section maximum of (3.0±0.8)×10−15 cm2 at 60 meV for SF6− formation, which is close to the gas phase value. For C6F6, we obtain a maximum value (4.8±1.2)×10−15 cm2 at 75 meV. In contrast to isolated gas phase molecules, where both ions are only observed in a very narrow energy range around 0 eV, SF6− resulting from electron attachment to clusters is observed up to 1.5 eV. The same is true for the condensed submonolayers, where charge localization is observed up to 1.5 eV for SF6. The extension of stable SF6− formation to much higher energies in condensed media is attributed to the transfer of intramolecular vibrational energy from SF6− to phonon vibrational modes of the Ar cluster or the Kr multilayer film. C6F6− formation is also observed up to 1.7 eV from clusters, but on the film, charge localization is only detected up to 0.7 eV. This difference is explained by the orientation of the C6F6 molecules on the rare gas film, which diminishes vibrational energy transfer to the phonon bath of the Kr lattice. Similar results are also obtained for the dimeric configurations of these molecules seeded into Ar clusters. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481516
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  • 8
    Electronic Resource
    Electronic Resource
    Low-energy electron-energy-loss spectroscopy of condensed acetone: Electronic transitions and resonance-enhanced vibrational excitations (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 6707-6715 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report electron-energy-loss spectroscopy, within the incident electron energy range 1 to 19 eV, of solid films of acetone condensed at 18 K. The strong Rydberg progressions, which usually dominate the spectra in the gas phase, are found to completely disappear in the solid phase. In the absence of these transitions, the remaining broad bands centered at 4.3, 4.5, 6.2, 8.7, and 9.8 eV energy loss can be assigned to the 1 3A2(n→π*), 1 1A2(n→π*), 1 3A1(π→π*), 1 3B1(σ→π*), and 2 3A2(σ→π*) valence electronic transition of acetone, respectively. A broad feature ranging from 11 to 16 eV and having a maximum around 13.8 eV is ascribed to several overlapping autoionizing excited states. From a comparison with infrared and Raman spectra, the energy-loss peaks observed below 1 eV are found to be due to excitation of the fundamental, overtone, and combination vibrational modes of the molecule. Their incident energy dependence is showing broad vibrational enhancement maxima at 4, 7, and 9 eV, which are attributed to the formation of single-particle or shape resonances of 2B1, 2A1, and 2A2 (or 2B2) symmetries, respectively. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481245
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  • 9
    Electronic Resource
    Electronic Resource
    Sample morphology and porosity in electron stimulated desorption: N2* from N2 adsorbed onto nanoscale ice films (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 3874-3881 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have measured the electron-stimulated desorption of metastable molecular nitrogen (N2*) from N2 condensed onto solid thin films of water of varying preparation. Structures seen in the N2* yield function permit the quantity of N2 at the film–vacuum interface to be monitored and hence allow one to study changes in the effective surface area of the water film. This latter quantity is itself related to the porosity of the film. When deposited onto porous water, N2 molecules penetrate into the film and throughout its pores covering their large surface area. Under these conditions, the signal of desorbing N2* particles is inversely proportional to the surface area of the pores. We present a simple model for N2 film growth on a porous film. Its mathematical formulation allows the pore area and pore volume of amorphous water films to be measured. The surface region of crystalline water films is also found to be rough. Moreover, the porosity of solid water films is found to be dependent on the substrate on which the film is grown. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1288029
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  • 10
    Electronic Resource
    Electronic Resource
    Effects of morphology on the low-energy electron stimulated desorption of O− from O2 deposited on benzene and water ices (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 4811-4818 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We investigate the effects of the geometrical structure (phase and porosity) of multilayer benzene films on the desorption of O− induced by 2–20 eV electron impact on varying quantities of absorbed O2. Differences in the yield of O− from O2 doped amorphous and crystalline benzene films are attributed to the ability of O2 to diffuse into the amorphous solid via pores and defects formed during its deposition at 20 K. In contrast, diffusion into crystalline benzene is limited and deposited O2 molecules remain at the surface of the film. Thermal desorption measurements support this analysis. The data are also compared with results of similar experiments for O2 on water. While it is apparent that some of the variation in O− yield observed from ice films is similarly related to morphology, a substantial suppression of the O− yield is likely to result from energy loss by electrons prior to dissociation. Quenching of intermediate O2− states by water ice may also contribute to this suppression in the range 5–12 eV. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1394733
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