Grain Surface Reactions in Molecular Clouds: The Effect of Cosmic Rays and Quantum Tunneling

Abstract

Grain-surface reactions play an essential role in interstellar chemistry, since dust grain catalyses reactions at its surface allowing for the formation of molecules. We used a chemical model in which both gas-phase and grain-surface reactions occur and studied particularly the diffusion mechanisms on the surface of the grains. Surface reactions can occur via thermal hopping when species cross over a potential barrier or via quantum tunneling when species cross through this barrier. We show that the thermal diffusion (hopping) can be much more efficient after a cosmic ray particle collides with a dust grain, heating it to a peak temperature of 70K. We present here the results of numerical simulations after including the quantum tunneling mechanism for species H, H2 and O and considering the effect of cosmic ray particle collision on the surface reactions. As a consequence, the gas-phase and grain-surface abundances are affected and we show that more complex molecules can be formed in molecular clouds.

12 pages, 24 figures

References in corpus (5)

• A Unified Representation of Gas-Phase Element Depletions in the Interstellar Medium
• Formation of methyl formate and other organic species in the warm-up phase of hot molecular cores
• Non-thermal desorption from interstellar dust grains via exothermic surface reactions
• Polycylcic Aromatic Hydrocarbons (PAH's) in dense cloud chemistry
• The effect of uncertainties on chemical models of dark clouds

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