Atmospheric Chemistry of Titan Options

[Juramike]

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.

[Juramike]

Dicyanoacetylene (C4N2) [NC-CC-CN]



Two different literature models have two different pathways to form dicyanoacetylene (C4H2). The route described in Krasnopolsky 2009 model has nitrile radical (.CN) attack the carbon-carbon triple bond of cyanoacetylene (HCC-CN). This makes an intermediate central double bond with one of the carbons holding an unpaired electron. Next door, the C-H bond cleaves, and hydrogen goes flying away as hydrogen radical (H.) and the resulting unpaired electron dives in with the carbon holding the unpaired electron and makes the central triple bond.

The Wilson and Atreya 2004 model proposes that two molecules of cyanomethylene carbene (:CH(CN)) connect their unpaired electons together to form a middle double bond. The resulting intermediate (1,2-dicyanoethylene), blows out H2 most likely in a concerted 4-electron pathway (2 sets of 2 paired electrons – this is a very typical concerted reaction, benzene resonances and [3,3]-sigmatropic rearrangements are 3 sets of 2 paired electrons (6 electron concerted pathways)) to give the final dicyanoacetylene and molecular hydrogen (H2).