Atmospheric Chemistry of Titan |
Atmospheric Chemistry of Titan |
May 2 2010, 03:38 AM
Post
#1
|
||
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/
|
|
|
||
Jun 13 2010, 03:21 AM
Post
#2
|
||
Senior Member Group: Moderator Posts: 2785 Joined: 10-November 06 From: Pasadena, CA Member No.: 1345 |
Ethylene (C2H4) [H2C=CH2]
Ethylene is a key intermediate that is a starting point for many pathways. If it's "inbound" is more than it's "outbound" there might be some that actually makes it down to the surface. But the Krasnopolsky 2009 model has a flux of zero - in that model it all gets used up. The starting point is the generation of an extremely reactive intermediate - a radical carbene. This results from a high energy photon doing an almost total fraggo number on methane. The force of that photon blows out atomic hydrogen and a hydrogen radical. The molecular hydrogen gives a clue that this part was a concerted 2-electron process and so the carbene is spin paired and in a singlet state (as drawn in the diagram). This is in contrast to the other possible case where three hydrogen radicals get blown out and the carbene is spin unpaired and is in a triplet state. The carbene can undergo a C-H insertion with a methane molecule (just wedging it's way between the C and the H) to make an ethyl radical transition state that probably only lasts a molecular vibration before kicking out a hydrogen radical and having both unpaired electrons dive into a double bond molecular pi-orbital. Et voila, ethylene is born! While this process seems really funky, according to the Krasnopolsky 2009 model, 75% of all ethylene production follows this pathway. Now that you've got ethylene, acetylene is only a UV photon away... -------------------- Some higher resolution images available at my photostream: http://www.flickr.com/photos/31678681@N07/
|
|
|
||
Lo-Fi Version | Time is now: 26th September 2024 - 01:57 PM |
RULES AND GUIDELINES Please read the Forum Rules and Guidelines before posting. IMAGE COPYRIGHT |
OPINIONS AND MODERATION Opinions expressed on UnmannedSpaceflight.com are those of the individual posters and do not necessarily reflect the opinions of UnmannedSpaceflight.com or The Planetary Society. The all-volunteer UnmannedSpaceflight.com moderation team is wholly independent of The Planetary Society. The Planetary Society has no influence over decisions made by the UnmannedSpaceflight.com moderators. |
SUPPORT THE FORUM Unmannedspaceflight.com is funded by the Planetary Society. Please consider supporting our work and many other projects by donating to the Society or becoming a member. |