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 22 2010, 01:13 AM
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Senior Member Group: Moderator Posts: 2785 Joined: 10-November 06 From: Pasadena, CA Member No.: 1345 |
Cyanoacetylene (HC3N) [HCC-CN]
The dominant mechanism (according to the Krasnopolsky 2009 model) is the reaction of nitrile radical (.CN) with acetylene. After the initial addition into the triple bond, the C-H bond of the secondary carbon breaks homolytically, and the hydrogen radical leaves the system, while the newly unpaired electron on the carbon jumps into an empty molecular pi-orbital with the other unpaired electron on the carbon radical to form a triple bond. According to the mode, 62% of the cyanoacetylene is formed by this route. However, there is another possible route to this molecule, again using our friend :CH(CN). In this case, photoionization of methane forms a high energy ionized intermediate CH3+ then undergoes electron recombination to violently produce .:CH. The Krasnopolsky model actually makes this occur in one step. Either way, you get methyne (the simplest carbyne) which then can react with methylene carbene. This could go a number of different ways, I’ve drawn the fully stepwise mechanism as if we were dealing with a triradical CH, and a diradical :CHCN. In the first step, a single bond is formed between the two carbon atoms. The resulting carbene-radical then combines to form a double bond to make a transient acrylonitrile radical. This kicks out a hydrogen radical (from the secondary carbon) as the resulting carbon radicals combine to form the triple bond (like the step above). -------------------- Some higher resolution images available at my photostream: http://www.flickr.com/photos/31678681@N07/
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