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  • 1
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    Field measurement of time to ponding (1997)
    In:  EPIC3Soil use and management, 13, pp. 24-28
    Details
    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 2
    Electronic Resource
    Electronic Resource
    Interaction of ammonia with chemically modified ruthenium (001) surfaces (1991)
    s.l. : American Chemical Society
    Langmuir 7 (1991), S. 1689-1694 
    Details
    ISSN: 1520-5827
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/la00056a021
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  • 3
    Electronic Resource
    Electronic Resource
    Interaction of ethylene with the ruthenium(001) surface (1986)
    s.l. : American Chemical Society
    Journal of the American Chemical Society 108 (1986), S. 3554-3562 
    Details
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ja00273a002
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  • 4
    Electronic Resource
    Electronic Resource
    Dynamics of recombinative desorption: Angular distributions of H2, HD, and D2 desorbing from Cu(111) (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 7499-7501 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have determined the angular distributions of H2, HD, and D2 desorbing from Cu(111) for surface temperatures in the range 370–800 K. These are found to be strongly peaked and symmetric about the surface normal in every case. Results for all three isotopes are found to be indistinguishable, being close to a cos 12θf distribution at 600 K, slightly narrower at 370 K, and slightly broader at 800 K. Results are discussed in terms of other previous desorption measurements and related to adsorption data via detailed balance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460181
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  • 5
    Electronic Resource
    Electronic Resource
    On the nature of trapping and desorption at high surface temperatures. Theory and experiments for the Ar–Pt(111) system (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 1516-1527 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report molecular dynamics calculations and molecular beam experiments on trapping and desorption as a function of surface temperature and initial gas conditions for the Ar–Pt(111) system. The trapping process involves very rapid equilibration of the normal component of incidence velocity but extremely slow accommodation of the parallel component. At high surface temperatures for which the residence time of Ar is sufficiently short (e.g., roughly 40 ps at 273 K), trapped atoms desorb before their incident parallel velocity is thermalized. Thus trapping in the usual sense of complete equilibration with the surface does not occur; instead these quasitrapped atoms are characterized by full accommodation of only the normal velocity component. In both simulations and experiments there is a range of temperatures for which the desorbing flux associated with quasitrapping is distinguishable from the flux due to direct inelastic scattering. These results are qualitatively reproduced by a simple model for the time-varying velocity distribution of quasitrapped atoms, which treats the different components of velocity independently.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460695
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  • 6
    Electronic Resource
    Electronic Resource
    Dynamics of the chemisorption of O2 on Pt(111): Dissociation via direct population of a molecularly chemisorbed precursor at high incidence kinetic energy (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 1626-1635 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have used the thermal desorption spectroscopy of the O/O2+CO→CO2 system to probe the chemical nature of oxygen that remains on a Pt(111) surface following exposure to a supersonic O2 beam under various conditions. We find that for a surface temperature of 90 K, the resulting CO2 formation thermal desorption spectrum is the same for all beam kinetic energies employed up to 1.1 eV at normal incidence, in all cases resembling that assigned to the O2+CO co-adsorbate system. This spectrum is clearly distinct from the O+CO case, where atomically chemisorbed oxygen is obtained either by thermal dissociation of O2 on the surface or by exposing the 90 K surface to a beam containing O atoms. These results imply that the dissociative chemisorption of O2 on Pt(111) proceeds by way of a molecular precursor even at relatively high incidence kinetic energies, at least as high as 1.1 eV. This interpretation readily accounts for the strong surface temperature dependence associated with dissociation under these conditions but contrasts with previous assignment of a direct (or quasidirect) dissociation process at high energies. We have also reexamined a number of previous observations in terms of this new picture, including the initial decline in dissociation probability with increasing kinetic energy. This falloff is attributed to a decrease in the trapping probability into a physisorption state, as recently suggested by Luntz et al. Considering the present results in the light of other recent studies, it now seems clear that the physisorption state is then a precursor to the molecular chemisorption state which can also be accessed directly at high kinetic energy. In this picture the molecular chemisorption state is then a precursor to dissociation even at high kinetic energy, and the dissociation probability depends on the (temperature-dependent) branching ratio between the dissociation and ultimate desorption of these species.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459966
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  • 7
    Electronic Resource
    Electronic Resource
    Trapping-mediated dissociative chemisorption of ethane on Ir(110)-(1×2) (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 4508-4512 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Evidence is presented to support a trapping-mediated dissociative chemisorption mechanism for ethane interacting with an Ir(110)-(1×2) surface. The data were obtained from supersonic molecular-beam measurements with an incident kinetic energy Ei ranging between 1.2 and 24.1 kcal/mol, a surface temperature Ts between 154 and 500 K, and an incident angle θi between 0° and 45°. For Ei less than approximately 13 kcal/mol, the probability of dissociative chemisorption S0 decreases rapidly with increasing Ts. For a surface temperature of 154 K, S0 decreases with increasing Ei for 1.2≤Ei ≤13.4 kcal/mol, consistent with a trapping-mediated chemisorption mechanism. Indeed, the data also support quantitatively a kinetic model consistent with a trapping-mediated chemisorption mechanism. The difference in the activation energies for desorption and chemisorption from the physically adsorbed, trapped state Ed −Ec is 2.2±0.2 kcal/mol. In the trapping-mediated regime, S0 is found to be rather insensitive to incident angle, scaling with Ei cos0.5 θi .
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457762
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  • 8
    Electronic Resource
    Electronic Resource
    Molecular adsorption of ethane on the Ir(110)-(1×2) surface: Monte Carlo simulations and molecular beam reflectivity measurements (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 1397-1406 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Experimental results, obtained using a molecular beam reflectivity method, for the probability of molecular physical adsorption of ethane on the Ir(110)-(1×2) surface are presented. We analyze these results using Monte Carlo simulations and show that molecular adsorption can occur either "directly'' or through a precursor state in which an ethane molecule is trapped in a second layer of molecularly adsorbed ethane with subsequent migration to a vacant site. From the Monte Carlo simulations, we are able to establish that the energy barrier for the desorption of an ethane molecule from the precursor state is approximately 4.5 kcal/mol. We also find that the energy barrier for diffusion of an ethane molecule on top of a monolayer of ethane molecularly adsorbed on the Ir(110)-(1×2) surface is approximately 3.7 kcal/mol.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458151
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  • 9
    Electronic Resource
    Electronic Resource
    Electron energy loss spectroscopy of ammonia on Ru(001) (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 5225-5236 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The adsorption of ammonia on Ru(001) has been studied using high-resolution electron energy loss spectroscopy. Multilayer, second-layer, and monolayer ammonia have been characterized vibrationally. These three states desorb near 115, 130 and between approximately 150 and 350 K, respectively. The symmetric deformation mode of chemisorbed ammonia shifts down in frequency continuously with increasing coverage from approximately 1160 cm−1 in the low-coverage limit to approximately 1070 cm−1 at (monolayer) saturation. The frequency of this mode in coordination compounds of ammonia is sensitive to the charge on the metal atom (increasing with increasing positive charge), and the frequency shift of this mode on the Ru(001) surface can be correlated with the work function decrease that this surface undergoes as the ammonia coverage increases. Off-specular EEL spectra allow the weak NH3 rocking mode and the frustrated translation of the ammonia perpendicular to the surface (i.e., the metal–nitrogen stretch) of chemisorbed ammonia to be resolved near 625 and 340 cm−1, respectively. These modes have not been identified in previous EELS studies of chemisorbed ammonia on hexagonally close-packed metal surfaces. Second-layer and multilayer ammonia yield EEL spectra similar to those observed on other metal surfaces. In agreement with previous results, the adsorption of ammonia on Ru(001) at 80 K, followed by annealing, leads only to reversible desorption.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454597
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  • 10
    Electronic Resource
    Electronic Resource
    Trapping of molecular ethane on the Ir(110)–(1×2) surface (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 3986-3988 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457808
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