Interplay of gas and ice during cloud evolution

Abstract

During the evolution of diffuse clouds to molecular clouds, gas-phase molecules freeze out on surfaces of small dust particles to form ices. On dust surfaces, water is the main constituent of the icy mantle in which a complex chemistry is taking place. We aim to study the formation pathways and the composition of the ices throughout the evolution of diffuse clouds. For this purpose, we use time-dependent rate equations to calculate the molecular abundances in both gas phase and on solid surfaces (onto dust grains). We fully consider the gas-dust interplay by including the details of freeze-out, chemical and thermal desorption, as well as the most important photo-processes on grain surfaces. The difference in binding energies of chemical species on bare and icy surfaces is also incorporated into our equations. Using the numerical code FLASH, we perform a hydrodynamical simulation of a gravitationally bound diffuse cloud and follow its contraction. We find that while the dust grains are still bare, water formation is enhanced by grain surface chemistry which is subsequently released into the gas phase, enriching the molecular medium. The CO molecules, on the other hand, tend to freeze out gradually on bare grains. This causes CO to be well mixed and strongly present within the first ice layer. Once one monolayer of water ice has formed, the binding energy of the grain surface changes significantly and an immediate and strong depletion of gas-phase water and CO molecules occur. While hydrogenation converts solid CO into formaldehyde (H${}_2$CO) and methanol (CH${}_3$OH), water ice becomes the main constituent of the icy grains. Inside molecular clumps formaldehyde is more abundant than water and methanol in the gas phase owing its presence in part to chemical desorption.

19 pages, 10 figures, 9 tables, 23 equations. Accepted for publication Astronomy & Astrophysics. In version 3: Language edit, added gas-phase reaction tables, title has changed

References in corpus (56)

• Dust Grain Size Distributions and Extinction in the Milky Way, LMC, and SMC
• Complex Chemistry in Star-Forming Regions: An Expanded Gas-Grain Warm-up Chemical Model
• Structure of Stationary Photodissociation Fronts
• The Relation Between Optical Extinction and Hydrogen Column Density in the Galaxy
• A KInetic Database for Astrochemistry (KIDA)
• The photodissociation and chemistry of CO isotopologues: applications to interstellar clouds and circumstellar disks
• The Universality of Turbulence in Galactic Molecular Clouds
• Non-thermal desorption from interstellar dust grains via exothermic surface reactions
• Burgers Turbulence
• Water, O2 and Ice in Molecular Clouds
• Protostellar Collapse with Various Metallicities
• Photodesorption of ices I: CO, N2 and CO2
• Extensible Component Based Architecture for FLASH, A Massively Parallel, Multiphysics Simulation Code
• On the Formation of CO2 and Other Interstellar Ices
• H3+ in Diffuse Interstellar Clouds: a Tracer for the Cosmic-Ray Ionization Rate
• Simulation of the Formation and Morphology of Ice Mantles on Interstellar Grains
• Water in Star-Forming Regions with the Herschel Space Observatory (WISH): Overview of key program and first results
• On the internal structure of starless cores. II. A molecular survey of L1498 and L1517B
• Photodesorption of water ice: a molecular dynamics study
• Formation of hydrogen peroxide and water from the reaction of cold hydrogen atoms with solid oxygen at 10K
• CO ice photodesorption: A wavelength-dependent study
• Surface chemistry in the interstellar medium - I - H2 formation by Langmuir-Hinshelwood and Eley-Rideal mechanisms
• Radiative transfer and the energy equation in SPH simulations of star formation
• The chemistry of vibrationally excited H2 in the interstellar medium
• The Different Structures of the Two Classes of Starless Cores
• Molecular dynamics study of photodissociation of water in crystalline and amorphous ice
• Water Formation through a Quantum Tunneling Surface Reaction, OH + H2, at 10 K
• The Polytropic Equation of State of Interstellar Gas Clouds
• Water formation on bare grains: When the chemistry on dust impacts interstellar gas
• CO2 formation in quiescent clouds; an experimental study of the CO + OH pathway
• The effect of dust cooling on low-metallicity star-forming clouds
• The IRAM-30m line survey of the Horsehead PDR: IV. Comparative chemistry of H2CO and CH3OH
• Molecular dynamics simulations of the ice temperature dependence of water ice photodesorption
• Evolution of dust in the Orion Bar with Herschel: I. Radiative transfer modelling
• Effects of primordial chemistry on the cosmic microwave background
• Chemistry and Radiative Transfer of Water in Cold, Dense Clouds
• Deep observations of O2 toward a low-mass protostar with Herschel-HIFI
• Dynamics of CO in Amorphous Water Ice Environments
• High CO depletion in southern infrared-dark clouds
• Gas-phase CO depletion and N2H+ abundances in starless cores
• Quantum tunneling of oxygen atoms on very cold surfaces
• Water and methanol in low-mass protostellar outflows: gas-phase synthesis, ice sputtering and destruction
• Widespread Methanol Emission from the Galactic Center
• Chemical stratification in the Orion Bar: JCMT Spectral Legacy Survey observations
• Gaseous CO Abundance---An Evolutionary Tracer for Molecular Clouds
• Influence of surface coverage on the chemical desorption process
• A (sub)millimetre study of dense cores in Orion B9
• The impact of X-rays on molecular cloud fragmentation and the IMF
• Star formation near an obscured AGN: Variations in the initial mass function
• Efficient Simulations of Interstellar Gas-Grain Chemistry Using Moment Equations
• The impact of freeze-out on collapsing molecular clouds
• The role of OH in the chemical evolution of protoplanetary disks. I. The comet-forming region
• The implications of dust for high-redshift protogalaxies and the formation of binary disks
• Impact of an accurate modeling of primordial chemistry in high resolution studies
• Enhanced H2O formation through dust grain chemistry in X-ray exposed environments
• Difference in the spatial distribution between H_2O and CO_2 ices in M82 found with AKARI

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• Where does the energy go during the interstellar NH${}_3$ formation on water ice? A computational study
• Study of the photon-induced formation and subsequent desorption of CH3 OH and H2 CO in interstellar ice analogs
• A detailed framework to incorporate dust in hydrodynamical simulations
• Establishing the evolutionary timescales of the massive star formation process through chemistry
• A novel framework to study the impact of binding energy distributions on the chemistry of dust grains
• How chemistry influences cloud structure, star formation, and the IMF
• Fast methods for tracking grain coagulation and ionization. I. Analytic derivation
• An Exploration of the Statistical Signatures of Stellar Feedback
• Rapid ortho-to-para nuclear spin conversion of H2 on a silicate dust surface
• The first frost in the Pipe Nebula
• Modeling the role of electron attachment rates on column density ratios for CnH-/CnH (n=4,6,8) in dense molecular clouds
• Modelling thermochemical processes in protoplanetary disks I: numerical methods
• A multigrain-multilayer astrochemical model with variable desorption energy for surface species
• The Cosmic-Ray Induced Sputtering Process On Icy Grains
• Species cycling and the enhancement of ammonia in prestellar cores
• CO Diffusion on Interstellar Amorphous Solid Water: A Computational Study
• The role of ices in star-forming clouds