Deuterated interstellar and circumstellar molecules: D/H ratio and dominant formation processes

Etim, EE and Akpan, NI and Adelagun, RAO and Lawal, U and Khanal, GP (2020) Deuterated interstellar and circumstellar molecules: D/H ratio and dominant formation processes. In: Indian Journal of Physics .

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Abstract

Abstract: There are several constraints associated with the different models used in accounting for the D/H ratio observed of singly and multiply deuterated interstellar and circumstellar molecular species. Thermodynamically, the most distinctive difference between a molecule and its deuterated analogue is the zero point energy (ZPE). Applying high level quantum chemical calculations, the ZPE for all H-containing and their corresponding D-analogues for all interstellar/circumstellar molecular species considered in this study are determined. From the difference in the ZPE between the H-containing and the corresponding D-analogue, Boltzmann factor is computed for all the systems using the excitation temperature/molecular cloud temperature for the known D-molecules and a range of temperature for others. From the results, there is a direct correlation between the Boltzmann factors and the D/H ratios. Pronounced deuterium fractionation occurs at larger values of Boltzmann factor resulting in the observed high D/H ratios. Increased deuterium fractionation at low temperature suggests that grain surface reactions are the major formation processes for deuterated molecules. This implies that at lower temperature (higher Boltzmann factor), the exchange reaction involving deuterium or deuterium fractionation is much pronounced resulting in the distribution and redistribution of deuterium among various species. The implications of these results and the possibility of detecting more D-molecules are discussed. Graphic abstract: Figure not available: see fulltext., © 2020, Indian Association for the Cultivation of Science.

Item Type:	Journal Article
Publication:	Indian Journal of Physics
Publisher:	Springer
Additional Information:	Copy right for this article belongs to Springer
Keywords:	Abundance; Molecules; Astrochemistry; Interstellar medium; Deuterium
Department/Centre:	Division of Chemical Sciences > Inorganic & Physical Chemistry
Date Deposited:	08 Jan 2021 10:21
Last Modified:	08 Jan 2021 10:21
URI:	http://eprints.iisc.ac.in/id/eprint/65773

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