Accurate rate coefficients for models of interstellar gas-grain chemistry

Abstract

The methodology for modeling grain-surface chemistry has been greatly improved by taking into account the grain size and fluctuation effects. However, the reaction rate coefficients currently used in all practical models of gas-grain chemistry are inaccurate by a significant amount. We provide expressions for these crucial rate coefficients that are both accurate and easy to incorporate into gas-grain models. We use exact results obtained in earlier work, where the reaction rate coefficient was defined by a first-passage problem, which was solved using random walk theory. The approximate reaction rate coefficient presented here is easy to include in all models of interstellar gas-grain chemistry. In contrast to the commonly used expression, the results that it provides are in perfect agreement with detailed kinetic Monte Carlo simulations. We also show the rate coefficient for reactions involving multiple species.

4 pages, 2 figures

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Cited by in corpus (8)

• Surface chemistry in the interstellar medium - I - H2 formation by Langmuir-Hinshelwood and Eley-Rideal mechanisms
• Formation of Complex Organic Molecules in Cold Interstellar Environments through non-diffusive grain-surface and ice-mantle chemistry
• Surface chemistry in the Interstellar Medium II. ${\mathrm{H}}_2$ formation on dust with random temperature fluctuations
• Binomial moment equations for stochastic reaction systems
• Kinetic Monte Carlo simulations of the grain-surface back-diffusion effect
• Diffusion-limited reactions on a two-dimensional lattice with binary disorder
• Excitation of Unidentified Infrared Bands by H atom impact
• Diffusion-limited reactions on disordered surfaces with continuous distributions of binding energies