Atmospheric Chemistry of Titan |
Atmospheric Chemistry of Titan |
May 2 2010, 03:38 AM
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Senior Member Group: Moderator Posts: 2785 Joined: 10-November 06 From: Pasadena, CA Member No.: 1345 |
Here is a "Benzene-O-Vision" graphic showing the amount of benzene and phenyl radicals at high altitudes on Titan. This is based on detections of benzene and phenyl radical (which recombined in the sample chamber to make benzene) using the INMS instrument during closest approach. The numbers are normalized to constant pressure altitude, roughly 1000 km.
The data was taken from Table 1 in: Vuitton et al, Journal of Geophysical Research 113 (2008) E05007. "Formation and distribution of benzene on Titan". doi: 10.1029/2007JE002997 [EDIT 5/24/10: Article freely available here] and overlaid on a map of Titan. The authors mentioned that the errors in these measurements are 20%. These detections are well above the detached haze layer. Most are at the same sun azimuth angle. (T23 observation had the lowest angle.) Assuming that the temporal difference is minimal (each dot is from a different flyby), there doesn't appear to be an obvious correlation with latitude. This graphic does show that benzene is present even waaaay up in the thermosphere and ionosphere. -------------------- Some higher resolution images available at my photostream: http://www.flickr.com/photos/31678681@N07/
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Jul 29 2010, 10:42 PM
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Senior Member Group: Moderator Posts: 2785 Joined: 10-November 06 From: Pasadena, CA Member No.: 1345 |
Acrylonitrile (C2H3CN) [H2C=CHCN]
This molecule also has two routes according to the Krasnopolsky 2009 model. In the first route ethyl radical adds to the CN triple bond of cyanide to make a new C-C single bond and an intermediate radical on the nitrogen. The nitrogen radical electron dives in while a C-H bond on the other side homolytically cleaves. The two electrons reform a CN triple bond and the resultant hydrogen radical goes flying off. The second route starts with cyanomethylene carbene (:CHCN). Reaction of this carbene with methyl radical (CH3) makes a new double bond as one of the electrons of the carbene (which may be in a triplet state) hooks up with the unpaired electron of the methyl radical. The resulting ethyl nitrile radical has the unpaired electron on the carbon alpha to the nitrile group. A C-H bond on the terminal carbon cleaves and one of the unpaired electrons joins the other unpaired electron to form a double bond. The other unpaired electron flies off with the hydrogen nucleus to be a hydrogen radical. Acrylonitrile is known to polymerize when a suitable base is added. On Earth, it is a major industrial chemical product (several million tons/year scale) used for making all sorts of plastics and polymers. On Titan's surface, if a large concentration of this were present, and with a suffficient thermal “kick” it could undergo polymerization or further reactions in the presence of a base such as an organic amine. (Polymerization from initial nucleophilic Michael addition (1,4-addition) to the beta-carbon, then the resulting enolate undergoes Michael addition to another molecule of acrylonitirile, etc.) -------------------- Some higher resolution images available at my photostream: http://www.flickr.com/photos/31678681@N07/
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