A Unified Monte Carlo Treatment of Gas-Grain Chemistry for Large Reaction Networks. I. Testing Validity of Rate Equations in Molecular Clouds

Abstract

In this study we demonstrate for the first time that the unified Monte Carlo approach can be applied to model gas-grain chemistry in large reaction networks. Specifically, we build a time-dependent gas-grain chemical model of the interstellar medium, involving about 6000 gas-phase and 200 grain surface reactions. This model is used to test the validity of the standard and modified rate equation methods in models of dense and translucent molecular clouds and to specify under which conditions the use of the stochastic approach is desirable. We found that at temperatures 25--30 K gas-phase abundances of H${}_2$O, NH${}_3$, CO and many other gas-phase and surface species in the stochastic model differ from those in the deterministic models by more than an order of magnitude, at least, when tunneling is accounted for and/or diffusion energies are 3x lower than the binding energies. In this case, surface reactions, involving light species, proceed faster than accretion of the same species. In contrast, in the model without tunneling and with high binding energies, when the typical timescale of a surface recombination is greater than the timescale of accretion onto the grain, we obtain almost perfect agreement between results of Monte Carlo and deterministic calculations in the same temperature range. At lower temperatures ($\sim 10$ K) gaseous and, in particular, surface abundances of most important molecules are not much affected by stochastic processes.

33 pages, 9 figures, 1 table. Accepted for publication in ApJ

References in corpus (9)

• Formation of methyl formate and other organic species in the warm-up phase of hot molecular cores
• Simulation of the Formation and Morphology of Ice Mantles on Interstellar Grains
• Photoprocesses in protoplanetary disks
• Modeling the Lukewarm Corino Phase - is L1527 unique?
• Gas-grain chemistry in cold interstellar cloud cores with a microscopic Monte Carlo approach to surface chemistry
• Chemistry in Protoplanetary Disks: A Sensitivity Analysis
• Cold CO Gas in Protoplanetary Disks
• Bistability in Interstellar Gas-Phase Chemistry
• Efficient Simulations of Interstellar Gas-Grain Chemistry Using Moment Equations

Cited by in corpus (37)

• Photochemistry and astrochemistry: photochemical pathways to interstellar complex organic molecules
• Reaction Networks For Interstellar Chemical Modelling: Improvements and Challenges
• Astrochemistry and compositions of planetary systems
• Chemistry in Disks. IV. Benchmarking gas-grain chemical models with surface reactions
• Chemical evolution of turbulent protoplanetary disks and the Solar nebula
• A Unified Monte Carlo Treatment of Gas-Grain Chemistry for Large Reaction Networks. II. A Multiphase Gas-Surface-Layered Bulk Model
• The HNC/HCN Ratio in Star-Forming Regions
• Chemical modelling of complex organic molecules with peptide-like bonds in star-forming regions
• Protoplanetary Disk Structure With Grain Evolution: the ANDES Model
• Binding Energy of Molecules on Water Ice: Laboratory Measurements and Modeling
• Impact of grain evolution on the chemical structure of protoplanetary disks
• Three-dimensional off-lattice Monte Carlo kinetics simulations of interstellar grain chemistry and ice structure
• Water delivery from cores to disks: deuteration as a probe of the prestellar inheritance of H2O
• Production of interstellar hydrogen peroxide (H2O2) on the surface of dust grains
• A Unified Microscopic-Macroscopic Monte Carlo Simulation of Gas-Grain Chemistry in Cold Dense Interstellar Clouds
• Interstellar Simulations Using A Unified Microscopic-Macroscopic Monte Carlo Model with a full Gas-Grain Network including Bulk Diffusion in Ice Mantles
• G11.92-0.61-MM2: A Bonafide Massive Prestellar Core?
• The Effects of Grain Size and Temperature Distributions on the Formation of Interstellar Ice Mantles
• Far-infrared study of tracers of oxygen chemistry in diffuse clouds
• X-ray induced chemistry of water and related molecules in low-mass protostellar envelopes
• Chemical modeling of Infrared Dark Clouds: the Role of Surface Chemistry
• Complex organic molecules along the accretion flow in isolated and externally irradiated protoplanetary disks
• Physical properties and chemical composition of the cores in the California molecular cloud
• A hybrid moment equation approach to gas-grain chemical modeling
• The effect of selective desorption mechanisms during interstellar ice formation
• Ethylene oxide and Acetaldehyde in hot cores
• Chemical modeling of the complex organic molecules in the extended region around Sagittarius B2
• Interstellar chemical differentiation across grain sizes
• The Influence of Deuteration and Turbulent Diffusion on the Observed D/H Ratio
• Machine learning-accelerated chemistry modeling of protoplanetary disks
• Effects of turbulent dust grain motion to interstellar chemistry
• Cosmic-ray-induced dissociation and reactions in warm interstellar ices
• Chempl: a playable package for modeling interstellar chemistry
• The physical and chemical structure of Sagittarius B2, VIII. Full molecular line survey of hot cores
• Photochemistry of interstellar ice forming Complex Organic Molecules
• Modelling carbon-chain species formation in lukewarm corinos with new multi-phase models
• A stochastic model and Monte Carlo algorithm for fluctuation-induced H${}_2$ formation on the surface of interstellar dust grains