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]

1-Butene (C4H8) [H2C=CHCH2CH3]



1-Butene is 1,3-butadiene's more saturated buddy. It has one double bond removed. To be fair, I'm not sure if this is the 1-butene isomer or the more thermodynamically preferred 2-butene, or the 2-methyl prop-1-ene isomer. (With four carbons, the iso-form is possible, it is the most stabilized double bond, and it makes the most sense mechanistically). Most likely, C4H8 would be a mixture of isomers. The mechanism will assume linear 1-butene is formed.

The sequence starts by the addition of hydrogen radical (atomic hydrogen) to allene to give allyl radical (C3H5). The middle carbon should be the best place to put the unpaired electron, but in order to form 1-butene, you need it on the end. Reaction of allyl radical with methyl radical at the C3 terminus gives 1-butene. The reaction of allyl radical with the unpaired electron at C2 (middle) should give the iso isomer - 2-methyl propene = isobutylene (not shown in the diagram). From 1-butene, a 1,3 H-shift would give more thermodynamically preferred 2-butene. However, 1-butene is perfectly stable at room temperatures on Earth. 2-butene can exist in two forms, cis and trans. In cis the two methyls are on the same side of the double bond, in trans they are opposite. Generally, the trans forms of a double bond is more stable. Both cis and trans forms of 2-butane are stable and separable at Earth room temperatures. Once formed they should also be stable at Titan temperatures. The formation mechanism should "lock in" the isomer. However, there is always the possibility that an excitation, or collision, or protonation/deprotonation with a superacid (like CH5+) can isomerize or switch the double bond geometry.

Next up is saturated n-butane.