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Title: CO DIFFUSION INTO AMORPHOUS H{sub 2}O ICES

Abstract

The mobility of atoms, molecules, and radicals in icy grain mantles regulates ice restructuring, desorption, and chemistry in astrophysical environments. Interstellar ices are dominated by H{sub 2}O, and diffusion on external and internal (pore) surfaces of H{sub 2}O-rich ices is therefore a key process to constrain. This study aims to quantify the diffusion kinetics and barrier of the abundant ice constituent CO into H{sub 2}O-dominated ices at low temperatures (15–23 K), by measuring the mixing rate of initially layered H{sub 2}O(:CO{sub 2})/CO ices. The mixed fraction of CO as a function of time is determined by monitoring the shape of the infrared CO stretching band. Mixing is observed at all investigated temperatures on minute timescales and can be ascribed to CO diffusion in H{sub 2}O ice pores. The diffusion coefficient and final mixed fraction depend on ice temperature, porosity, thickness, and composition. The experiments are analyzed by applying Fick’s diffusion equation under the assumption that mixing is due to CO diffusion into an immobile H{sub 2}O ice. The extracted energy barrier for CO diffusion into amorphous H{sub 2}O ice is ∼160 K. This is effectively a surface diffusion barrier. The derived barrier is low compared to current surface diffusion barriers inmore » use in astrochemical models. Its adoption may significantly change the expected timescales for different ice processes in interstellar environments.« less

Authors:
 [1]; ;  [2];  [3]; ;  [4]
  1. Department of Chemistry, University of Virginia, Charlottesville, VA 22904 (United States)
  2. Theoretical Chemistry, Institute for Molecules and Materials, Radboud University Nijmegen, Heyendaalseweg 135, 6525 AJ Nijmegen (Netherlands)
  3. Department of Chemistry, Wellesley College, Wellesley, MA 02481 (United States)
  4. Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States)
Publication Date:
OSTI Identifier:
22522530
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 801; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
74 ATOMIC AND MOLECULAR PHYSICS; 79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ASTROPHYSICS; ATOMS; CARBON DIOXIDE; CARBON MONOXIDE; CHEMISTRY; COMPARATIVE EVALUATIONS; DESORPTION; DIFFUSION; DIFFUSION BARRIERS; DIFFUSION EQUATIONS; ICE; INTERSTELLAR SPACE; MOBILITY; MOLECULES; RADICALS; TIME DEPENDENCE; WATER

Citation Formats

Lauck, Trish, Karssemeijer, Leendertjan, Cuppen, Herma M., Shulenberger, Katherine, Rajappan, Mahesh, and Öberg, Karin I., E-mail: tlauck@virginia.edu, E-mail: koberg@cfa.harvard.edu. CO DIFFUSION INTO AMORPHOUS H{sub 2}O ICES. United States: N. p., 2015. Web. doi:10.1088/0004-637X/801/2/118.
Lauck, Trish, Karssemeijer, Leendertjan, Cuppen, Herma M., Shulenberger, Katherine, Rajappan, Mahesh, & Öberg, Karin I., E-mail: tlauck@virginia.edu, E-mail: koberg@cfa.harvard.edu. CO DIFFUSION INTO AMORPHOUS H{sub 2}O ICES. United States. doi:10.1088/0004-637X/801/2/118.
Lauck, Trish, Karssemeijer, Leendertjan, Cuppen, Herma M., Shulenberger, Katherine, Rajappan, Mahesh, and Öberg, Karin I., E-mail: tlauck@virginia.edu, E-mail: koberg@cfa.harvard.edu. Tue . "CO DIFFUSION INTO AMORPHOUS H{sub 2}O ICES". United States. doi:10.1088/0004-637X/801/2/118.
@article{osti_22522530,
title = {CO DIFFUSION INTO AMORPHOUS H{sub 2}O ICES},
author = {Lauck, Trish and Karssemeijer, Leendertjan and Cuppen, Herma M. and Shulenberger, Katherine and Rajappan, Mahesh and Öberg, Karin I., E-mail: tlauck@virginia.edu, E-mail: koberg@cfa.harvard.edu},
abstractNote = {The mobility of atoms, molecules, and radicals in icy grain mantles regulates ice restructuring, desorption, and chemistry in astrophysical environments. Interstellar ices are dominated by H{sub 2}O, and diffusion on external and internal (pore) surfaces of H{sub 2}O-rich ices is therefore a key process to constrain. This study aims to quantify the diffusion kinetics and barrier of the abundant ice constituent CO into H{sub 2}O-dominated ices at low temperatures (15–23 K), by measuring the mixing rate of initially layered H{sub 2}O(:CO{sub 2})/CO ices. The mixed fraction of CO as a function of time is determined by monitoring the shape of the infrared CO stretching band. Mixing is observed at all investigated temperatures on minute timescales and can be ascribed to CO diffusion in H{sub 2}O ice pores. The diffusion coefficient and final mixed fraction depend on ice temperature, porosity, thickness, and composition. The experiments are analyzed by applying Fick’s diffusion equation under the assumption that mixing is due to CO diffusion into an immobile H{sub 2}O ice. The extracted energy barrier for CO diffusion into amorphous H{sub 2}O ice is ∼160 K. This is effectively a surface diffusion barrier. The derived barrier is low compared to current surface diffusion barriers in use in astrochemical models. Its adoption may significantly change the expected timescales for different ice processes in interstellar environments.},
doi = {10.1088/0004-637X/801/2/118},
journal = {Astrophysical Journal},
number = 2,
volume = 801,
place = {United States},
year = {Tue Mar 10 00:00:00 EDT 2015},
month = {Tue Mar 10 00:00:00 EDT 2015}
}