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Atmospheric Chemistry of Titan
Juramike
post May 2 2010, 03:38 AM
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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.

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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.


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Juramike
post May 6 2010, 01:50 PM
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The radical cationic, carbonium, and carbenium species up in the atmosphere are high energy intermediates. They can exist up there (and in the MS sample chambers) because they are in rarefied environments. They don't bump into other molecules that often.

As these compounds descend in the atmosphere, they will encounter other molecules, bump into things more often, and be able to exchange energies and react much, much better. When you get down to the surface (or in solution) there are a lot of opportunities for molecules to react and find a happy equilibrium. High-energy structures will be just fleeting intermediates on the way to more more stable molecule. They won't be able to last more than a molecular vibration before they bump into something and react or transfer their energy.

'Course at Titan's low temperatures, some of the metastable high-energy compounds might get trapped out in a matrix and not be able to react. One of the best ways to keep things from reacting is to cool it down, putting it in the freezer so to speak and keep it from getting over the energy hump to the next state. If there is a high energy transition state with higher activation energies away from it, you can freeze it out. (IIRC, carbenes [think of it as "methylene diradical" or :CH2] has been studied in a frozen Argon matrix).


I'm not real sure about the Lunine abstract....methane is very non-polar and would not be happy solvating a carbocation. I think it would be EXTREMELY difficult for methane to spontaneously dissociate to a carbocation-hydride. (This doesn't happen in the lab at terrestrial temperatures.) But if a carbocation (or superacid) was plopped or sprinkled into a lake, it would do something.

Definitely not comfortable with referring to normal methane (CH4) as a "protic" solvent. That implies that methane is able to donate a proton. (CH4--> -:CH3 + H+). With a pKa of 45, that won't happen.

BUT (and I think this is where the abstract is going) if a stronger superacid was sprinkled into a lake, the proton affinities might force methane to take on a proton and make CH5+ (again, methane is not happy about this.) Proton affinities show the clear progression CH4-->CH3-CH3->acetylene-->ethylene-->H2O--<ammonia. (Table here: Wikipedia/Proton Affinity (data page)). So if CH5 (or H3+) was dribbled into a lake it would eventually work itself down the chain to protonating water to make hydronium. (Dunno the proton affinity for clathrate, but I assume it's similar or slightly less than water, protonation should break up the clatrate matrix - that would be a neat and "easy" experiment to try.) The ultimate sink on Titan should be ammonia to generate ammonium ion.


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Littlebit
post May 11 2010, 09:22 PM
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QUOTE (Juramike @ May 6 2010, 06:50 AM) *
This is enough to blast an electron out of the molecular (or even atomic) orbital and create a wierd little species called a radical cation. This is a single electron process, so one of the electrons in the molecule is now unpaired, thus a radical. It is also charged positively, since an electron was ripped out of the system. Radical cations are pretty exotic here on Earth. They are usually only found in the vacuum ionization chamber of your local LCMS or GCMS. They do very weird things.

Is methane+ a right wing or left wing radical?


Enjoy your posts, as always Juramike - we are still out here!
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Posts in this topic
- Juramike   Atmospheric Chemistry of Titan   May 2 2010, 03:38 AM
- - Juramike   Into the Wierdness: Ion-neutral chemistry (A maj...   May 5 2010, 02:59 AM
- - ngunn   Thanks for that very interesting explanation Mike....   May 6 2010, 11:20 AM
- - Juramike   The radical cationic, carbonium, and carbenium spe...   May 6 2010, 01:50 PM
|- - Littlebit   QUOTE (Juramike @ May 6 2010, 06:50 AM) T...   May 11 2010, 09:22 PM
|- - ngunn   QUOTE (Littlebit @ May 11 2010, 10:22 PM)...   May 11 2010, 09:56 PM
- - Juramike   Cute. To be really, really anal, a radical shoul...   May 12 2010, 12:30 AM
- - Juramike   Purple Haze or Where It’s At A paper by Lavvas et...   May 12 2010, 11:46 PM
|- - rlorenz   QUOTE (Juramike @ May 12 2010, 06:46 PM) ...   May 20 2010, 07:17 PM
- - Juramike   Titan's organic chemistry is driven by photoch...   May 16 2010, 09:52 PM
- - Juramike   Titan's Chaotic Chemistry Titan is a syntheti...   May 18 2010, 12:30 AM
- - Juramike   Many ways to fall Below is a graphic showing an e...   May 20 2010, 04:17 AM
- - Juramike   I agree that the reality is probably a lot more co...   May 21 2010, 05:42 PM
- - Juramike   It turns out that the methane is only part of the ...   May 31 2010, 04:57 AM
- - Juramike   In the presence of N2 or Ar, ionization occurs fir...   Jun 1 2010, 03:36 AM
|- - Littlebit   QUOTE (Juramike @ May 31 2010, 08:36 PM) ...   Jun 1 2010, 07:59 PM
- - Juramike   Nitrogen does get incorporated. It is primarily i...   Jun 1 2010, 08:34 PM
- - Juramike   So what does CH5+ do? Basically(!), not much....   Jun 2 2010, 04:15 AM
- - Juramike   Even on electron quenching of the CH5+ radical, it...   Jun 3 2010, 03:32 AM
- - ngunn   About Titan chemistry, not necessarily atmospheric...   Jun 3 2010, 09:01 PM
- - Juramike   Great catch!! From the press release: ...   Jun 4 2010, 12:38 AM
- - Bill Harris   Mike, This has been a good discussion of the chem...   Jun 4 2010, 10:02 PM
- - Juramike   The low temperatures at the surface and lower atmo...   Jun 4 2010, 10:49 PM
- - Juramike   For the moment, the Clark et al. paper can be foun...   Jun 4 2010, 10:52 PM
- - Juramike   Article in press: Strobel, D.F. Icarus (2010) Art...   Jun 6 2010, 07:58 PM
- - Juramike   H2 is the key reagent that shunts the pathway to t...   Jun 8 2010, 12:43 AM
- - Juramike   Titan’s atmospheric chemistry is driven by sunligh...   Jun 9 2010, 02:16 AM
- - remcook   Starting on Monday: http://fd147.univ-rennes1.fr/a...   Jun 9 2010, 07:04 AM
- - Juramike   Very cool! Here is an EXCEL conditional forma...   Jun 10 2010, 02:58 AM
|- - rlorenz   QUOTE (Juramike @ Jun 9 2010, 09:58 PM) H...   Jun 12 2010, 01:00 AM
|- - Juramike   As requested (twice now) here is a comparison of s...   Aug 25 2010, 01:41 AM
- - Bill Harris   This is mindboggling. The potential scope of the...   Jun 10 2010, 02:31 PM
- - Shaka   Will the final exam be essay or multiple choice?   Jun 10 2010, 11:59 PM
- - Juramike   I'm gonna give away the answers!   Jun 11 2010, 12:30 AM
- - Juramike   Enter the mechanism Over the next several graphic...   Jun 11 2010, 05:51 AM
- - Bill Harris   QUOTE (Juramike @ Jun 10 2010, 07:30 PM) ...   Jun 11 2010, 04:13 PM
- - Juramike   Ethane (C2H6) [CH3CH3] Almost all ethane is for...   Jun 12 2010, 03:40 AM
- - Juramike   Ethylene (C2H4) [H2C=CH2] Ethylene is a key inter...   Jun 13 2010, 03:21 AM
- - Juramike   Acetylene (C2H2) [HCCH] Acetylene has several for...   Jun 14 2010, 02:52 AM
- - Juramike   Methyl acetylene (1-propyne) (C3H4) [CH3CCH] This...   Jun 15 2010, 02:58 AM
- - jekbradbury   QUOTE (Juramike @ Jun 14 2010, 10:58 PM) ...   Jun 15 2010, 07:35 PM
- - Juramike   Whoops. You are right, it is allene not cumene. ...   Jun 15 2010, 10:39 PM
- - Juramike   [Well, whaddya know...cyclopropenone has been dete...   Jun 16 2010, 09:28 PM
- - Juramike   Ethyl radical (.C2H5) [.CH2CH3] - key intermediate...   Jun 17 2010, 01:46 AM
- - Bill Harris   Mike, one thing I notice is that many of the react...   Jun 17 2010, 02:47 AM
- - Juramike   H+?? Dangit. Those should all be H. hydrogen r...   Jun 17 2010, 03:03 AM
- - Bill Harris   Oh, H-radical as in "H-dot"? They look...   Jun 17 2010, 05:08 AM
- - Juramike   Alright y'all, I'm real sorry about this, ...   Jun 19 2010, 03:06 AM
- - Juramike   Propane (C3H8) [CH3CH2CH3] The straightforward ...   Jun 19 2010, 03:21 AM
- - Juramike   Went back and fixed all diagrams in the different ...   Jun 19 2010, 12:45 PM
- - Bill Harris   Looks good, Mike. Sorry to have tossed a monkey w...   Jun 20 2010, 07:18 PM
- - Juramike   Diacetylene (C4H2) [HCC-CCH] - also known as Buta...   Jun 22 2010, 10:59 PM
- - Juramike   1,3-Butadiene (C4H6) [H2C=CHCHCH=CH2] The forma...   Jun 25 2010, 04:39 AM
- - PDP8E   Mike, you had me at H2O pdp8e   Jun 25 2010, 04:52 AM
|- - Juramike   QUOTE (PDP8E @ Jun 25 2010, 12:52 AM) Mik...   Jun 26 2010, 05:00 AM
- - Juramike   1-Butene (C4H8) [H2C=CHCH2CH3] 1-Butene is 1,3-...   Jun 26 2010, 04:57 AM
- - Juramike   n-Butane (C4H10) [CH3CH2CH2CH3] Boring butane c...   Jun 29 2010, 04:03 AM
- - Juramike   Benzene (C6H6) At lower altitudes, benzene is f...   Jun 30 2010, 03:56 AM
- - Juramike   Benzene (C6H6) high altitude ion route At highe...   Jul 1 2010, 12:31 AM
- - Juramike   Structure of Benzenium (C6H7+) This is one of t...   Jul 2 2010, 12:46 AM
- - Juramike   Beyond Benzene - PAH's and Polyphenyls Polyar...   Jul 4 2010, 01:46 AM
- - Bill Harris   The genesis of Titan's atmosphere may be more ...   Jul 8 2010, 12:44 PM
- - Juramike   HCN The incorporation of nitrogen into Titan’s ...   Jul 13 2010, 12:00 AM
- - Juramike   .CN radical - key intermediate The formation of...   Jul 14 2010, 12:11 AM
- - Juramike   Cyanomethlyene carbene [:CH(CN)] A very recent...   Jul 19 2010, 12:03 AM
- - GEmin   QUOTE The first experimental evidence showing how ...   Jul 19 2010, 06:36 AM
- - Juramike   Acetonitrile (CH3CN) There are multiple ways to...   Jul 21 2010, 02:08 AM
- - Juramike   Cyanoacetylene (HC3N) [HCC-CN] The dominant mec...   Jul 22 2010, 01:13 AM
- - Juramike   Cyanogen (C2N2) [NC-CN] According to the Krasno...   Jul 23 2010, 12:17 PM
- - Juramike   Dicyanoacetylene (C4N2) [NC-CC-CN] Two differen...   Jul 25 2010, 04:04 PM
- - Juramike   Acrylonitrile (C2H3CN) [H2C=CHCN] This molecule...   Jul 29 2010, 10:42 PM
- - Juramike   I’ve tried to represent Titan’s chemistry in a sli...   Aug 2 2010, 03:02 AM
- - Juramike   The graphic below shows the pattern of dominant re...   Aug 22 2010, 08:06 PM
- - Juramike   Estimated depths solids vs. liquids from the vario...   Aug 25 2010, 02:25 AM
- - Juramike   A recent DPS abstract discusses some possibilities...   Oct 8 2010, 02:26 PM
- - titanicrivers   Thanks for the discussion and the link Mike. One ...   Oct 8 2010, 03:46 PM
- - Juramike   Most of the formation chemistry seems to be happen...   Oct 8 2010, 05:21 PM
- - Juramike   LPSC 2011 abstract describes continuing efforts to...   Jan 30 2011, 04:07 AM
- - Juramike   Detection of high altitude cirrus clouds in Titan...   Feb 3 2011, 07:01 PM
- - centsworth_II   This gives hope of much greater understanding of T...   Feb 9 2011, 04:32 PM
- - ngunn   Interesting link posted on the Cassini Huygens Yah...   May 10 2011, 10:56 AM
- - Juramike   The Cool Way to PAH's in Titan's Upper Atm...   Jul 3 2011, 12:55 AM
- - scalbers   I saw a talk given at the AGU conference last week...   Dec 11 2011, 08:39 PM
- - Paolo   not sure this is the best topic to post it to, thi...   Jan 5 2012, 10:51 AM


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