Relevance of silicate surface morphology in interstellar H<inf>2</inf> formation. Insights from quantum chemical calculations

Javier Navarro-Ruiz, José Ángel Martínez-González, Mariona Sodupe, Piero Ugliengo, Albert Rimola

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11 Citations (Scopus)

Abstract

© 2015 The Authors. The adsorption of H atoms and their recombination to form an H2 molecule on slab models of the crystalline Mg2SiO4 forsterite (001) and (110) surfaces was studied by means of quantum mechanical calculations based on periodic density functional theory (DFT). Present results are compared with those previously reported for the most stable (010) surface, showing the relevance of the surface morphology and their stability on the H2 formation. Different H chemisorption states were identified, mostly on the outermost O atoms of the surfaces. In agreement with the higher instability of the (001) and (110) surfaces, the calculated adsorption energies are larger than those for the (010) surface. Computed energy barriers for the H hopping on these surfaces are exceedingly high to occur at the very low temperatures of deep space. For the adsorption of two H atoms, the most stable complexes are those in which the H atoms form Mg-H and SiOH surface groups. From these complexes, we did not identify energetically feasible paths for H2 formation through a Langmuir-Hinshelwood mechanism on the (001) surface because the initial states are more stable than the final products. However, on the (110) surface one path was found to be exoergic with very low energy barriers. This differs to that observed for the (010) surface, for which two feasible Langmuir-Hinshelwoodbased channels were identified. H2 formation through the Eley-Rideal mechanism was also simulated, in which an incoming H atom impinges on a pre-adsorbed H atom at the (001) and (110) surfaces in a barrierless way.
Original languageEnglish
Pages (from-to)914-924
JournalMonthly Notices of the Royal Astronomical Society
Volume453
Issue number1
DOIs
Publication statusPublished - 24 Jul 2015

Keywords

  • Astrochemistry
  • ISM: clouds
  • ISM: molecules
  • Molecular processes

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