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Physical Adsorption of Hydrogen on Interstellar Graphite Grain Surfaces

  • R. F. Willis
  • B. Fitton
Conference paper
Part of the Astrophysics and Space Science Library book series (ASSL, volume 55)

Abstract

We review existing single-particle theories concerning parameters of importance which determine the kinetics of hydrogen molecule formation and ejection from cold (T gr≲20 K) graphite grain surfaces. The nature of the single-particle quantum states of low mass gas atoms and molecules in a periodic surface lattice potential is considered. Contributions to the physical adsorption potential due to dynamic polarizability effects arising from the long-range collective valence-electron charge-density oscillations (plasmons) of the substrate are discussed. Short-range electron correlation effects at the surface may lead to the formation of a ‘quasimolecular state’ of adsorbed H2 with a bond length ∼3.5 Å and a reduced bond energy ∼0.075 eV. It is proposed, that one consequence of this dynamical screening of the adsorbed molecules is that they are ejected normal to the grain surface with velocities ≲20 km s−1 and not necessarily in a high vibrational state. Similar dynamical effects could be important in determining activation processes and long-range ordering in monolayer films of adsorbed H2. The astrophysical consequences of these many-body effects are discussed in the light of recent experimental and observational results.

Keywords

Kcal Mole Physical Adsorption Adsorption Energy Graphite Surface Adsorption Potential 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© D. Reidel Publishing Company, Dordrecht, Holland 1976

Authors and Affiliations

  • R. F. Willis
    • 1
  • B. Fitton
    • 1
  1. 1.Surface Physics Group, Astronomy Division, European Space Research OrganisationESTECNoordwijkHolland

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