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Evolution of CO on Titan

Wong, Ah-San and Morgan, Christopher G. and Yung, Yuk L. and Owen, Tobias (2002) Evolution of CO on Titan. Icarus, 155 (2). pp. 382-392. ISSN 0019-1035. doi:10.1006/icar.2001.6720.

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The early evolution of Titan's atmosphere is expected to produce enrichment in the heavy isotopomers of CO, ^(13)CO and C^(18)O, relative to ^(12)C^(16)O. However, the original isotopic signatures may be altered by photochemical reactions. This paper explains why there is no isotopic enrichment in C in Titan's atmosphere, despite significant enrichment of heavy H, N, and O isotopes. We show that there is a rapid exchange of C atoms between the CH_4 and CO reservoirs, mediated by the reaction ^1CH_2+^*CO→^(1*)CH_2+CO, where ^*C is ^(13)C. Based on recent laboratory measurements, we estimate the rate coefficient for this reaction to be 3.2×10^(−12) cm^3 s^(−1) at the temperature appropriate for the upper atmosphere of Titan. We investigate the isotopic dilution of CO using the Caltech/JPL one-dimensional photochemical model of Titan. Our model suggests that the time constant for isotopic exchange through the above reaction is about 800 Myr, which is significantly shorter than the age of Titan, and therefore any original isotopic enhancement of ^(13)C in CO may have been diluted by the exchange process. In addition, a plausible model for the evolution history of CO on Titan after the initial escape is proposed.

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Yung, Yuk L.0000-0002-4263-2562
Additional Information:© 2002 Elsevier Science (USA). Received May 11, 2001; revised July 12, 2001. Available online 12 April 2002. We thank F. S. Rowland for an illuminating discussion of the ^1CH_2 and CO reaction and W. B. DeMore and K. Bayes for valuable advice on the kinetics of hydrocarbons and CO.We thank Nicolas Biver for carrying out the observations of Titan with the JCMT and J. I. Moses for providing the code on which the Titan model is based. M. Allen provided critical inputs to a preliminary version of the paper, resulting in the present paper. We thank M. A. Gurwell and M. F. Gerstell for comments and suggestions. This research was supported in part by NAG5-6263 and the Cassini Project. C.G.M. thanks the National Research Council for an NRC Postdoctoral Fellowship.
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Cassini ProjectUNSPECIFIED
National Research Council (NRC) Postdoctoral FellowshipUNSPECIFIED
Issue or Number:2
Record Number:CaltechAUTHORS:20140821-075531138
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Official Citation:Ah-San Wong, Christopher G. Morgan, Yuk L. Yung, Tobias Owen, Evolution of CO on Titan, Icarus, Volume 155, Issue 2, February 2002, Pages 382-392, ISSN 0019-1035, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:48756
Deposited By: Ruth Sustaita
Deposited On:22 Aug 2014 06:11
Last Modified:10 Nov 2021 18:35

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