Diffusive vs. non-diffusive paths to interstellar hydrogen peroxide. A machine learning-based molecular dynamics study

Abstract

Context. Radical chemical reactions on cosmic dust grains play a crucial role in forming various chemical species. Among different radicals, the hydroxyl (OH) is one of the most important ones, with a rather specific chemistry. Aims. The goal of this work is to simulate the recombination dynamics of hydroxyl radicals and the subsequent formation of hydrogen peroxide (H${}_2$O${}_2$). Mthods. We employed neural network potentials trained on ONIOM(QM/QM) data, combining multi-reference (CASPT2) and density functional theory (DFT) calculations. This approach allows us to model the recombination of hydroxyl radicals on ice surfaces with high computational efficiency and accuracy. Results. Our simulations reveal that the initial position of the radicals plays a decisive role in determining recombination probability. We found that the formation of hydrogen-bond between radicals, competes with the formation of hydrogen peroxide, reducing the recombination efficiency, contrary to expectancy. This competition reduces the recombination probability for radicals that are initially formed approximately 3 Å apart. Recombination probabilities also depend on the kinetic energy of the added radicals, with values around 0.33 for thermal radicals and a wide range of values between 0.33 and 1.00 for suprathermal OH radicals. Conclusions. Based on our calculations we provide recommendations for introducing OH radical recombination into kinetic astrochemical models, differentiating between thermal and suprathermal radicals. The recombination behavior varies significantly between these two cases: while thermal radicals are sometimes trapped in hydrogen-bonded minima, the case of suprathermal radicals varies with the added energy. Our most important conclusion is that OH radical recombination probability cannot be assumed 1.0 for a wide variety of cases.

Accepted for publication in Astronomy and Astrophysics

References in corpus (31)

• Escaping free-energy minima
• PLUMED 2: New feathers for an old bird
• PLUMED: a portable plugin for free-energy calculations with molecular dynamics
• Observations of the Icy Universe
• The Spitzer ice legacy: Ice evolution from cores to protostars
• Photochemistry and astrochemistry: photochemical pathways to interstellar complex organic molecules
• An Ice Age JWST inventory of dense molecular cloud ices
• Interstellar water chemistry: from laboratory to observations
• Laboratory evidence for efficient water formation in interstellar ices
• The Spatial Distribution of Complex Organic Molecules in the L1544 Pre-stellar Core
• Dust as interstellar catalyst I. Quantifying the chemical desorption process
• Experimental evidence for water formation on interstellar dust grains by hydrogen and oxygen atoms
• Formation of Complex Organic Molecules in Cold Interstellar Environments through non-diffusive grain-surface and ice-mantle chemistry
• Water formation at low temperatures by surface O2 hydrogenation II: the reaction network
• On Cosmic Ray-Driven Grain Chemistry in Cold Core Models
• Gas-grain chemistry in cold interstellar cloud cores with a microscopic Monte Carlo approach to surface chemistry
• Water formation at low temperatures by surface O2 hydrogenation I: characterization of ice penetration
• Gaussian Moments as Physically Inspired Molecular Descriptors for Accurate and Scalable Machine Learning Potentials
• Prevalence of Complex Organic Molecules in Starless and Prestellar Cores within the Taurus Molecular Cloud
• Quantum mechanical simulations of the radical-radical chemistry on icy surfaces
• Quantum tunneling during interstellar surface-catalyzed formation of water: the reaction H + H${}_2$O${}_2$ $\to$ H${}_2$O + OH
• Atom Tunneling in the Water Formation Reaction H${}_2$ + OH $\to$ H${}_2$O + H on an Ice Surface
• Fast and Sample-Efficient Interatomic Neural Network Potentials for Molecules and Materials Based on Gaussian Moments
• Diffusion activation energy and desorption activation energy for astrochemically relevant species on water ice show no clear relation
• Neural-Network Assisted Study of Nitrogen Atom Dynamics on Amorphous Solid Water. I. Adsorption & Desorption
• On the relevance of the H2 + O reaction pathway for the surface formation of interstellar water - A combined experimental and modeling study
• Behavior of Hydroxyl Radicals on Water Ice at Low Temperatures
• Reaction dynamics on amorphous solid water surfaces using interatomic machine learned potentials. Microscopic energy partition revealed from the P + H -> PH reaction
• Direct Determination of the Activation Energy for Diffusion of OH Radicals on Water Ice
• Enhanced formation of interstellar complex organic molecules on carbon monoxide ice
• A New Method for Simulating Photoprocesses in Astrochemical Models

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