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)


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.


Kcal Mole Physical Adsorption Adsorption Energy Graphite Surface Adsorption Potential 
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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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