The Effective Surface Area of Amorphous Solid Water Measured by the Infrared Absorption of Carbon Monoxide

Abstract

The need to characterize ices coating dust grains in dense interstellar clouds arises from the importance of ice morphology in facilitating the diffusion and storage of radicals and reaction products in ices, a well-known place for the formation of complex molecules. Yet, there is considerable uncertainty about the structure of ISM ices, their ability to store volatiles and under what conditions. We measured the infrared absorption spectra of CO on the pore surface of porous amorphous solid water (ASW), and quantified the effective pore surface area of ASW. Additionally, we present results obtained from a Monte Carlo model of ASW in which the morphology of the ice is directly visualized and quantified. We found that 200 ML of ASW annealed to 20 K has a total pore surface area that is equivalent to 46 ML. This surface area decreases linearly with temperature to about 120 K. We also found that (1) dangling OH bonds only exist on the surface of pores; (2) almost all of the pores in the ASW are connected to the vacuum--ice interface, and are accessible for adsorption of volatiles from the gas phase; there are few closed cavities inside ASW at least up to a thickness of 200 ML; (3) the total pore surface area is proportional to the total 3-coordinated water molecules in the ASW in the temperature range 60--120 K. We also discuss the implications on the structure of ASW and surface reactions in the ice mantle in dense clouds.

12 pages, 16 figures

References in corpus (5)

• The cometary composition of a protoplanetary disk as revealed by complex cyanides
• The origin of complex organic molecules in prestellar cores
• Discovery of interstellar ketenyl (HCCO), a surprisingly abundant radical
• Pore evolution in interstellar ice analogues: simulating the effects of temperature increase
• Characterization of thin film CO${}_2$ ice through the infrared ${\nu }_1+{\nu }_3$ combination mode

Cited by in corpus (5)

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• Refractive index and extinction coefficient of vapor-deposited water ice in the UV-Vis range
• Methoxymethanol Formation Starting from CO-Hydrogenation
• Laboratory-based sticking coefficients for ices on a variety of small grains analogs
• Infrared multiple-angle incidence resolution spectrometry for vapor-deposited amorphous water