A COMPREHENSIVE STUDY OF HYDROGEN ADSORBING TO AMORPHOUS WATER ICE: DEFINING ADSORPTION IN CLASSICAL MOLECULAR DYNAMICS

ABSTRACT Gas-grain and gas-phase reactions dominate the formation of molecules in the interstellar medium (ISM). Gas-grain reactions require a substrate (e.g., a dust or ice grain) on which the reaction is able to occur. The formation of molecular hydrogen (H2) in the ISM is the prototypical example...

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Bibliographic Details
Published in:The Astrophysical journal 2016-11, Vol.831 (1), p.54
Main Authors: Dupuy, John L., Lewis, Steven P., Stancil, P. C.
Format: Article
Language:English
Subjects:
ABUNDANCE
ADSORPTION
Astrophysics
ASTROPHYSICS, COSMOLOGY AND ASTRONOMY
ATOMS
Coefficients
Computer simulation
COSMIC DUST
Dust
dust, extinction
HYDROGEN
Hydrogen atoms
ICE
Interstellar chemistry
Interstellar gas
Interstellar matter
Interstellar medium
INTERSTELLAR SPACE
ISM: abundances
Kinetic energy
Molecular dynamics
MOLECULAR DYNAMICS METHOD
molecular processes
MOLECULES
PROBABILITY
SIMULATION
SUBSTRATES
SURFACES
WATER
Water ice
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Summary:ABSTRACT Gas-grain and gas-phase reactions dominate the formation of molecules in the interstellar medium (ISM). Gas-grain reactions require a substrate (e.g., a dust or ice grain) on which the reaction is able to occur. The formation of molecular hydrogen (H2) in the ISM is the prototypical example of a gas-grain reaction. In these reactions, an atom of hydrogen will strike a surface, stick to it, and diffuse across it. When it encounters another adsorbed hydrogen atom, the two can react to form molecular hydrogen and then be ejected from the surface by the energy released in the reaction. We perform in-depth classical molecular dynamics simulations of hydrogen atoms interacting with an amorphous water-ice surface. This study focuses on the first step in the formation process; the sticking of the hydrogen atom to the substrate. We find that careful attention must be paid in dealing with the ambiguities in defining a sticking event. The technical definition of a sticking event will affect the computed sticking probabilities and coefficients. Here, using our new definition of a sticking event, we report sticking probabilities and sticking coefficients for nine different incident kinetic energies of hydrogen atoms [5-400 K] across seven different temperatures of dust grains [10-70 K]. We find that probabilities and coefficients vary both as a function of grain temperature and incident kinetic energy over the range of 0.99-0.22.
ISSN:0004-637X
1538-4357
DOI:10.3847/0004-637X/831/1/54