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Dynamic Deuterium Enrichment in Cometary Water Via ELEY–RIDEAL Reactions

Yao, Yunxi and Giapis, Konstantinos P. (2017) Dynamic Deuterium Enrichment in Cometary Water Via ELEY–RIDEAL Reactions. Astrophysical Journal, 835 (1). Art. No. 67. ISSN 0004-637X. doi:10.3847/1538-4357/835/1/67.

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The deuterium-to-hydrogen ratio (D/H) in water found in the coma of Jupiter family comet (JFC) 67P/Churyumov–Gerasimenko was reported to be (5.3 ± 0.7) × 10^(−4), the highest among comets and three times the value for other JFCs with an ocean-like ratio. This discrepancy suggests the diverse origins of JFCs and clouds the issue of the origin of Earth's oceanic water. Here we demonstrate that Eley–Rideal reactions between accelerated water ions and deuterated cometary surface analogs can lead to instantaneous deuterium enrichment in water scattered from the surface. The reaction proceeds with H2O+ abstracting adsorbed D atoms, forming an excited H_2DO^* state, which dissociates subsequently to produce energetic HDO. Hydronium ions are also produced readily by the abstraction of H atoms, consistent with H_3O^+ detection and abundance in various comets. Experiments with water isotopologs and kinematic analysis on deuterated platinum surfaces confirmed the dynamic abstraction mechanism. The instantaneous fractionation process is independent of the surface temperature and may operate on the surface of cometary nuclei or dust grains, composed of deuterium-rich silicates and carbonaceous chondrites. The requisite energetic water ions have been detected in the coma of 67P in two populations. This dynamic fractionation process may temporarily increase the water D/H ratio, especially as the comet gets closer to the Sun. The magnitude of the effect depends on the water ion energy-flux and the deuterium content of the exposed cometary surfaces.

Item Type:Article
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Yao, Yunxi0000-0002-0814-6675
Giapis, Konstantinos P.0000-0002-7393-298X
Additional Information:© 2017 American Astronomical Society. Received 2016 October 4. Accepted 2016 December 8. Published 2017 January 19. This report was based on work funded by the NSF (Award No. 1202567).
Funding AgencyGrant Number
Subject Keywords:astrochemistry; comets: general; methods: laboratory: molecular; molecular processes
Issue or Number:1
Record Number:CaltechAUTHORS:20170125-143516366
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Official Citation:Yunxi Yao and Konstantinos P. Giapis 2017 ApJ 835 67
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:73731
Deposited By: Ruth Sustaita
Deposited On:25 Jan 2017 23:35
Last Modified:11 Nov 2021 05:21

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