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On Cosmic Ray-Driven Grain Chemistry in Cold Core Models

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Abstract

In this paper, we present preliminary results illustrating the effect of cosmic rays on solid-phase chemistry in models of both TMC-1 and several sources with physical conditions identical to TMC-1 except for hypothetically enhanced ionization rates. Using a recent theory for the addition of cosmic ray-induced reactions to astrochemical models, we calculated the radiochemical yields, called $$G$$ values, for the primary dust grain ice-mantle constituents. We show that the inclusion of this non-thermal chemistry can lead to the formation of complex organic molecules from simpler ice-mantle constituents, even under cold core conditions. In addition to enriching ice-mantles, we find that these new radiation-chemical processes can lead to increased gas-phase abundances as well, particularly for HOCO, NO$$_2$$, HC$$_2$$O, methyl formate (HCOOCH$$_3$$), and ethanol (CH$$_3$$CH$$_2$$OH). These model results imply that HOCO - and perhaps NO$$_2$$ - might be observable in TMC-1. Future detections of either of these two species in cold interstellar environments could provide strong support for the importance of cosmic ray-driven radiation chemistry. The increased gas-phase abundance of methyl formate can be compared with abundances achieved through other formation mechanisms such as pure gas-phase chemistry and three-body surface reactions.

Most cited references2

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The Formation and Depletion of Molecules in Dense Interstellar Clouds

(1973)
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Energetic Charged-Particle Interactions with Atmospheres and Surfaces

(1990)
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Author and article information

Journal
15 May 2018
Article
1805.05764