Direct Determination of the Activation Energy for Diffusion of OH Radicals on Water Ice

Abstract

Using a combination of photostimulated desorption and resonance-enhanced multiphoton ionization methods, the behaviors of OH radicals on the surface of interstellar ice analog was monitored at temperatures between 54 and 80 K. The OH number density on the surface of ultraviolet (UV)-irradiated compact amorphous solid water gradually decreased at temperatures above 60 K. Analyzing the temperature dependence of OH intensities with the Arrhenius equation, the decrease can be explained by recombination of two OH radicals, which is rate-limited by thermal diffusion of OH. The activation energy for surface diffusion was experimentally determined for the first time to be 0.14 +/- 0.01 eV, which is larger than or equivalent to those assumed in theoretical models. This value implies that the diffusive reaction of OH radicals starts to be activated at approximately 36 K on interstellar ice.

5 figures, Accepted to ApJL

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Cited by in corpus (8)

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• Proposed importance of HOCO chemistry: Inefficient formation of CO${}_2$ from CO and OH reactions on ice dust
• Molecular Mobility of Extraterrestrial Ices: Surface Diffusion in Astrochemistry and Planetary Science
• Determination of the branching ratio of CH${}_3$OH + OH reaction on water ice surface at 10 K
• Pathways to Interstellar Amides via Carbamoyl (NH2CO) Isomers by Radical-Neutral Reactions on Ice Grain Mantles
• Diffusive vs. non-diffusive paths to interstellar hydrogen peroxide. A machine learning-based molecular dynamics study
• Isotopomer-Specific Carbon Isotope Ratio of Complex Organic Molecules in Star-Forming Cores
• Photodesorption efficiency of OH radical on the ice surface in the wavelength range from ultraviolet to visible