Abstract
Within the framework of The Heterogeneous dust Evolution Model for Interstellar Solids (THEMIS), this work explores the surface processes and chemistry relating to core/mantle interstellar and cometary grain structures and their influence on the nature of these fascinating particles. It appears that a realistic consideration of the nature and chemical reactivity of interstellar grain surfaces could self-consistently and within a coherent framework explain: the anomalous oxygen depletion, the nature of the CO dark gas, the formation of ‘polar ice’ mantles, the red wing on the 3 μm water ice band, the basis for the O-rich chemistry observed in hot cores, the origin of organic nano-globules and the 3.2 μm ‘carbonyl’ absorption band observed in comet reflectance spectra. It is proposed that the reaction of gas phase species with carbonaceous a-C(:H) grain surfaces in the interstellar medium, in particular the incorporation of atomic oxygen into grain surfaces in epoxide functional groups, is the key to explaining these observations. Thus, the chemistry of cosmic dust is much more intimately related with that of the interstellar gas than has previously been considered. The current models for interstellar gas and dust chemistry will therefore most likely need to be fundamentally modified to include these new grain surface processes.
Highlights
Interstellar dust has been something of a problem for more than 80 years, ever since the early measurements of interstellar reddening by Trumpler [1]
It appears that a realistic consideration of the nature and chemical reactivity of interstellar grain surfaces could self-consistently and within a coherent framework explain: the anomalous oxygen depletion, the nature of the CO dark gas, the formation of ‘polar ice’ mantles, the red wing on the 3 μm water ice band, the basis for the O-rich chemistry observed in hot cores, the origin of organic nano-globules and the 3.2 μm ‘carbonyl’ absorption band observed in comet reflectance spectra
The paper is organized as follows: §2 discusses carbon depletion and accretion from the gas, the nature of core/mantle grains, C-shine and mantle evolution, §3 considers the consequences of dust evolution, accretion anomalies, surface chemistry and surface epoxide and aziridine functional groups, grain surface carbonyl groups and CO sequestration from the gas, §4 discusses the role of evolved grain mantles, ‘organic’ materials and nano-globules, ‘volatile ice’ mantles, photolysis effects, hot core processing, comets and chemistry, §5 suggests some experiments that might be used to explore the ideas proposed here and §6 concludes this work
Summary
Interstellar dust has been something of a problem for more than 80 years, ever since the early measurements of interstellar reddening by Trumpler [1]. This work is an attempt to provide a global framework within which to link and interpret, in a selfconsistent and coherent manner, a wide diversity of open questions within the sphere of interstellar dust research These relate to the observational and laboratory analyses of:. The paper is organized as follows: §2 discusses carbon depletion and accretion from the gas, the nature of core/mantle grains, C-shine and mantle evolution, §3 considers the consequences of dust evolution, accretion anomalies, surface chemistry and surface epoxide and aziridine functional groups, grain surface carbonyl groups and CO sequestration from the gas, §4 discusses the role of evolved grain mantles, ‘organic’ materials and nano-globules, ‘volatile ice’ mantles, photolysis effects, hot core processing, comets and chemistry, §5 suggests some experiments that might be used to explore the ideas proposed here and §6 concludes this work
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