Interstellar Simulations Using A Unified Microscopic-Macroscopic Monte Carlo Model with a full Gas-Grain Network including Bulk Diffusion in Ice Mantles

Abstract

We have designed an improved algorithm that enables us to simulate the chemistry of cold dense interstellar clouds with a full gas-grain reaction network. The chemistry is treated by a unified microscopic-macroscopic Monte Carlo approach that includes photon penetration and bulk diffusion. To determine the significance of these two processes, we simulate the chemistry with three different models. In Model 1, we use an exponential treatment to follow how photons penetrate and photodissociate ice species throughout the grain mantle. Moreover, the products of photodissociation are allowed to diffuse via bulk diffusion and react within the ice mantle. Model 2 is similar to Model 1 but with a slower bulk diffusion rate. A reference Model 0, which only allows photodissociation reactions to occur on the top two layers, is also simulated. Photodesorption is assumed to occur from the top two layers in all three models. We found that the abundances of major stable species in grain mantles do not differ much among these three models, and the results of our simulation for the abundances of these species agree well with observations. Likewise, the abundances of gas-phase species in the three models do not vary. However, the abundances of radicals in grain mantles can differ by up to two orders of magnitude depending upon the degree of photon penetration and the bulk diffusion of photodissociation products. We also found that complex molecules can be formed at temperatures as low as 10 K in all three models.

Accepted for publication in ApJ

References in corpus (26)

• Formation of methyl formate and other organic species in the warm-up phase of hot molecular cores
• The Spitzer ice legacy: Ice evolution from cores to protostars
• A three-phase chemical model of hot cores: the formation of glycine
• Photodesorption of Ices II: H2O and D2O
• The c2d Spitzer spectroscopic survey of ices around low-mass young stellar objects II: CO2
• Photodesorption of ices I: CO, N2 and CO2
• Reactive Desorption and Radiative Association as Possible Drivers of Complex Molecule Formation in the Cold Interstellar Medium
• On the Formation of CO2 and Other Interstellar Ices
• Chemistry in Disks. IV. Benchmarking gas-grain chemical models with surface reactions
• Master Equation for Hydrogen Recombination on Grain Surfaces
• Photodesorption of water ice: a molecular dynamics study
• Mapping ices in protostellar environments on 1000 AU scales: Methanol-rich ice in the envelope of Serpens SMM 4
• Multilayer modeling of porous grain surface chemistry I. The GRAINOBLE model
• Microscopic simulation of methanol and formaldehyde ice formation in cold dense cores
• A Unified Monte Carlo Treatment of Gas-Grain Chemistry for Large Reaction Networks. II. A Multiphase Gas-Surface-Layered Bulk Model
• A new modified-rate approach for gas-grain chemical simulations
• Laboratory H2O:CO2 ice desorption data: entrapment dependencies and its parameterization with an extended three-phase model
• Gas-grain chemistry in cold interstellar cloud cores with a microscopic Monte Carlo approach to surface chemistry
• Quantification of segregation dynamics in ice mixtures
• A Unified Monte Carlo Treatment of Gas-Grain Chemistry for Large Reaction Networks. I. Testing Validity of Rate Equations in Molecular Clouds
• Three-dimensional off-lattice Monte Carlo kinetics simulations of interstellar grain chemistry and ice structure
• A Unified Microscopic-Macroscopic Monte Carlo Simulation of Gas-Grain Chemistry in Cold Dense Interstellar Clouds
• Moment equations for chemical reactions on interstellar dust grains
• Episodic Explosions in Interstellar Ices
• A hybrid moment equation approach to gas-grain chemical modeling
• Modeling the processing of interstellar ices by energetic particles

Cited by in corpus (32)

• Gas and grain chemical composition in cold cores as predicted by the Nautilus 3-phase model
• Formation of complex organic molecules in cold objects: the role of gas phase reactions
• Atom addition reactions in interstellar ice analogues
• Formation of complex organic molecules in hot molecular cores through nondiffusive grain-surface and ice-mantle chemistry
• Chemical modelling of complex organic molecules with peptide-like bonds in star-forming regions
• Efficient Production of S${}_8$ in Interstellar Ices: The effects of cosmic ray-driven radiation chemistry and non-diffusive bulk reactions
• Water deuteration and ortho-to-para nuclear spin ratio of H2 in molecular clouds formed via the accumulation of HI gas
• CO diffusion into amorphous H2O ices
• Adsorption energies of carbon, nitrogen, and oxygen atoms on the low-temperature amorphous water ice: A systematic estimation from quantum chemistry calculations
• Impulsive Spot Heating and Thermal Explosion of Interstellar Grains Revisited
• Atom Tunneling in the Water Formation Reaction H${}_2$ + OH $\to$ H${}_2$O + H on an Ice Surface
• Chemical and physical characterization of collapsing low-mass prestellar dense cores
• Unified Microscopic-Macroscopic Monte Carlo Simulations of Complex Organic Molecule Chemistry in Cold Cores
• Depletion of heavy nitrogen in the cold gas of star-forming regions
• A three-phase approach to grain surface chemistry in protoplanetary disks: Gas, ice surfaces and ice mantles of dust grains
• A New and Simple Approach to Determine the Abundance of Hydrogen Molecules on Interstellar Ice Mantles
• A new model of the chemistry of ionizing radiation in solids: CIRIS
• VLT/ISAAC infrared spectroscopy of embedded high-mass YSOs in the Large Magellanic Cloud: Methanol and the 3.47 micron band
• Importance of tunneling in H-abstraction reactions by OH radicals: The case of CH4 + OH studied through isotope-substituted analogs
• CO diffusion and desorption kinetics in CO${}_2$ ices
• The effect of selective desorption mechanisms during interstellar ice formation
• Tracing the atomic nitrogen abundance in star-forming regions with ammonia deuteration
• Chemical modeling of the complex organic molecules in the extended region around Sagittarius B2
• Interstellar chemical differentiation across grain sizes
• Chempl: a playable package for modeling interstellar chemistry
• Effect of stochastic grain heating on cold dense clouds chemistry
• Modelling carbon-chain species formation in lukewarm corinos with new multi-phase models
• Impact of an Active Sgr A* on the Synthesis of Water and Organic Molecules Throughout the Milky Way
• A multigrain-multilayer astrochemical model with variable desorption energy for surface species
• Low-temperature chemistry between water and hydroxyl radicals: H/D isotopic effects
• Isotopic fractionation in interstellar molecules
• Ice Chemistry Modeling of Active Phase Comets: Hale-Bopp