Atom Tunneling in the Water Formation Reaction H${}_2$ + OH $\to$ H${}_2$O + H on an Ice Surface

Abstract

OH radicals play a key role as an intermediate in the water formation chemistry of the interstellar medium. For example the reaction of OH radicals with H${}_2$ molecules is among the final steps in the astrochemical reaction network starting from O, O${}_2$, and O${}_3$. Experimentally it was shown that even at 10 K this reaction occurs on ice surfaces. As the reaction has a high activation energy only atom tunneling can explain such experimental findings. In this study we calculated reaction rate constants for the title reaction on a water-ice I${}_h$ surface. To our knowledge, low-temperature rate constants on a surface are not available in the literature. All surface calculations were done using a QM/MM framework (BHLYP/TIP3P) after a thorough benchmark of different density functionals and basis sets to highly accurate correlation methods. Reaction rate constants are obtained using instanton theory which takes atom tunneling into account inherently, with constants down to 110 K for the Eley-Rideal mechanism and down to 60 K for the Langmuir-Hinshelwood mechanism. We found that the reaction is nearly temperature independent below 80 K. We give kinetic isotope effects for all possible deuteration patterns for both reaction mechanisms. For the implementation in astrochemical networks, we also give fit parameters to a modified Arrhenius equation. Finally, several different binding sites and binding energies of OH radicals on the I${}_h$ surface are discussed and the corresponding rate constants are compared to the gas-phase case.

Published online. Supporting information on http://pubs.acs.org/doi/suppl/10.1021/acsearthspacechem.7b00052

References in corpus (13)

• Simulation of the Formation and Morphology of Ice Mantles on Interstellar Grains
• Laboratory evidence for efficient water formation in interstellar ices
• Atom-Tunneling in Chemistry
• Formation of hydrogen peroxide and water from the reaction of cold hydrogen atoms with solid oxygen at 10K
• Gas-grain chemistry in cold interstellar cloud cores with a microscopic Monte Carlo approach to surface chemistry
• Water Formation through a Quantum Tunneling Surface Reaction, OH + H2, at 10 K
• Formation of the prebiotic molecule NH${}_2$CHO on astronomical amorphous solid water surfaces: accurate tunneling rate calculations
• Water delivery from cores to disks: deuteration as a probe of the prestellar inheritance of H2O
• Quantum tunneling during interstellar surface-catalyzed formation of water: the reaction H + H${}_2$O${}_2$ $\to$ H${}_2$O + OH
• Interstellar Simulations Using A Unified Microscopic-Macroscopic Monte Carlo Model with a full Gas-Grain Network including Bulk Diffusion in Ice Mantles
• On the relevance of the H2 + O reaction pathway for the surface formation of interstellar water - A combined experimental and modeling study
• Importance of tunneling in H-abstraction reactions by OH radicals: The case of CH4 + OH studied through isotope-substituted analogs
• Rate constants from instanton theory via a microcanonical approach

Cited by in corpus (25)

• Water in star-forming regions (WISH): Physics and chemistry from clouds to disks as probed by Herschel spectroscopy
• A non-energetic mechanism for glycine formation in the interstellar medium
• The Case of H${}_2$C${}_3$O Isomers, Revisited: Solving the Mystery of the Missing Propadienone
• Laboratory and Computational Studies of Interstellar Ices
• Tunneling Reaction Kinetics for the Hydrogen Abstraction Reaction H + H${}_2$S -> H${}_2$ + HS in the Interstellar Medium
• Formation of complex organic molecules on interstellar CO ices? Insights from computational chemistry simulations
• Neural-Network Assisted Study of Nitrogen Atom Dynamics on Amorphous Solid Water. I. Adsorption & Desorption
• Influence of surface and bulk water ice on the reactivity of a water-forming reaction
• Radical Addition and H Abstraction Reactions in C2H2, C2H4 and C2H6: A Gateway for Ethyl and Vinyl Bearing Molecules in the Interstellar Medium
• Diastereoselective Formation of trans-HC(O)SH Through Hydrogenation of OCS on Interstellar Dust Grains
• A cryogenic ice setup to simulate carbon atom reactions in interstellar ices
• Methane formation in cold regions from carbon atoms and molecular hydrogen
• Hydrogen abstraction reactions in formic and thioformic acid isomers by hydrogen and deuterium atoms. Insights on isomerism and deuteration
• Cracking the Puzzle of CO2 Formation on Interstellar Ices. Quantum Chemical and Kinetic Study of the CO + OH -> CO2 + H Reaction
• Extension of the HCOOH and CO2 solid-state reaction network during the CO freeze-out stage: inclusion of H2CO
• Hydrogenation of small aromatic heterocycles at low temperatures
• Low-Temperature Kinetic Isotope Effects in CH3OH+H -> CH2OH+H2 Shed Light on the Deuteration of Methanol in Space
• Enhanced formation of interstellar complex organic molecules on carbon monoxide ice
• Divide-and-Conquer Method for Instanton Rate Theory
• Processing of hydroxylamine, NH2OH, an important prebiotic precursor, on interstellar ices
• The role of atom tunneling in gas-phase reactions in planet-forming disks
• Hydrogenation of acetaldehyde on interstellar ice analogs reveals limited destruction
• Diffusive vs. non-diffusive paths to interstellar hydrogen peroxide. A machine learning-based molecular dynamics study
• Investigating the impact of reactions of C and CH with molecular hydrogen on a glycine gas-grain network
• Superhydrogenation of indene at low temperatures