Abstract
The role and importance of nanoparticles for interstellar chemistry and beyond is explored within the framework of The Heterogeneous dust Evolution Model for Interstellar Solids (THEMIS), focusing on their active surface chemistry, the effects of nitrogen doping and the natural selection of interesting nanoparticle sub-structures. Nanoparticle-driven chemistry, and in particular the role of intrinsic epoxide-type structures, could provide a viable route to the observed gas phase OH in tenuous interstellar clouds en route to becoming molecular clouds. The aromatic-rich moieties present in asphaltenes probably provide a viable model for the structures present within aromatic-rich interstellar carbonaceous grains. The observed doping of such nanoparticle structures with nitrogen, if also prevalent in interstellar dust, could perhaps have important and observable consequences for surface chemistry and the formation of precursor pre-biotic species.
Highlights
The smaller end of the interstellar dust size distribution, which extends from micrometres down to sub-nanometre sizes, is at the heart of many important astrophysical processes, such as: the ultraviolet extinction that shields molecules from photo-dissociation, the origin of the IR emission bands, the anomalous microwave emission assumed to come from spinning nanoparticles, the heating of the gas through photoelectric emission and the catalytic formation of molecular hydrogen
The paper is organized as follows: §2 briefly describes the fundamentals of the assumed dust model (THEMIS), §3 focuses on the nature of interstellar nanoparticles, §4 considers the active chemistry of nanoparticle surfaces, §5 investigates the role of nitrogen atom doping in 3 carbonaceous nanograins, §6 speculates on the nature and natural selection of possibly pre-biotic aromatic-type moieties and §7 concludes this work
Given that the observational evidence points to the dominance of aromatic-richparticles to explain the dust IR-mm emission features and continuum in the tenuous interstellar medium (ISM), where there is little extinction, it would seem that FUV photolysis is favoured over the effects of hydrogenation [4,13,26] but that with increasing extinction the balance would shift in favour of hydrogenation [100]
Summary
The smaller end of the interstellar dust size distribution, which extends from micrometres down to sub-nanometre sizes, is at the heart of many important astrophysical processes, such as: the ultraviolet extinction that shields molecules from photo-dissociation, the origin of the IR emission bands, the anomalous microwave emission assumed to come from spinning nanoparticles, the heating of the gas through photoelectric emission and the catalytic formation of molecular hydrogen. The physical properties of nanoparticles are treated using a top-down extrapolation of the properties of bulk materials extended down to nanometre sizes [6,7,51,52,53,54] Such an approach is over-simplistic because the size-dependent properties of interstellar analogue materials [3] can help us to self-consistently understand and explain many of the critical observable properties of dust in the ISM [4,6,7,13,55]. The paper is organized as follows: §2 briefly describes the fundamentals of the assumed dust model (THEMIS), §3 focuses on the nature of interstellar nanoparticles, §4 considers the active chemistry of nanoparticle surfaces, §5 investigates the role of nitrogen atom doping in 3 carbonaceous nanograins, §6 speculates on the nature and natural selection of possibly pre-biotic aromatic-type moieties and §7 concludes this work
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