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Dissociative Recombination of Protonated Formic Acid: Implications for Molecular Cloud and Cometary Chemistry
Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
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2010 (Engelska)Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 709, nr 2, s. 1429-1434Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

At the heavy ion storage ring CRYRING in Stockholm, Sweden, we have investigated the dissociative recombination of DCOOD2+ at low relative kinetic energies, from similar to 1 meV to 1 eV. The thermal rate coefficient has been found to follow the expression k(T) = 8.43 x 10(-7) (T/300)(-0.78) cm(3) s(-1) for electron temperatures, T, ranging from similar to 10 to similar to 1000 K. The branching fractions of the reaction have been studied at similar to 2 meV relative kinetic energy. It has been found that similar to 87% of the reactions involve breaking a bond between heavy atoms. In only 13% of the reactions do the heavy atoms remain in the same product fragment. This puts limits on the gas-phase production of formic acid, observed in both molecular clouds and cometary comae. Using the experimental results in chemical models of the dark cloud, TMC-1, and using the latest release of the UMIST Database for Astrochemistry improves the agreement with observations for the abundance of formic acid. Our results also strengthen the assumption that formic acid is a component of cometary ices.

Ort, förlag, år, upplaga, sidor
2010. Vol. 709, nr 2, s. 1429-1434
Nyckelord [en]
astrochemistry; molecular processes
Nationell ämneskategori
Atom- och molekylfysik och optik
Identifikatorer
URN: urn:nbn:se:su:diva-43009DOI: 10.1088/0004-637X/709/2/1429ISI: 000273579800071OAI: oai:DiVA.org:su-43009DiVA, id: diva2:352913
Tillgänglig från: 2010-09-23 Skapad: 2010-09-23 Senast uppdaterad: 2017-12-12Bibliografiskt granskad
Ingår i avhandling
1. Dissociative recombination of organic molecular ions of relevance for interstellar clouds and Titan's upper atmosphere
Öppna denna publikation i ny flik eller fönster >>Dissociative recombination of organic molecular ions of relevance for interstellar clouds and Titan's upper atmosphere
2010 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

This thesis presents experimental studies on the dissociative recombination (DR) of the organic molecular ions CD3CND+, CH2CHCNH+, CH3CH2CNH+, CD3CDO+, CH3CHO+ and DCOOD2+. The experiments were all performed at the heavy ion storage ring CRYRING at the Manne Siegbahn Laboratory in Stockholm, Sweden. DR is the process in which a singly charged molecular cation captures a free electron, forming a highly excited intermediate molecule which then dissociates into exclusively neutral fragments. The process plays an important role as a plasma neutralizing mechanism in many cold, low density plasmas such as those encountered in planetary ionospheres and interstellar clouds. DR can also act as the final step in the gas-phase synthesis of different neutral molecules in such environments.

Our experimental findings indicate that nitriles that are lost by protonation in Titan’s upper atmosphere or in interstellar clouds to a large extent may be recycled by DR. Also, it appears that the DR of nitrile ions does not break the C-N bond, which supports the hypothesis that nitriles which are formed in Titan’s upper atmosphere do not degrade to recover N2. For the studied acetaldehyde cations, CD3CDO+ and CH3CHO+, we observed a considerable isotopic effect in the cross section, with the lighter isotopologue being more reactive. In the DR of DCOOD2+ an upper limit of only 13% for the branching fraction of the DCOOD + D channel was found. This finding has pronounced effects on the predicted abundance of formic acid in dark clouds.

Ort, förlag, år, upplaga, sidor
Stockholm: Department of Physics, Stockholm University, 2010. s. 70
Nyckelord
Dissociative recombination, Astrochemistry
Nationell ämneskategori
Fysik
Forskningsämne
kemisk fysik
Identifikatorer
urn:nbn:se:su:diva-43372 (URN)978-91-7447-133-5 (ISBN)
Disputation
2010-11-26, sal FB42, AlbaNova Universitetscentrum, Roslagstullsbacken 21, Stockholm, 10:00 (Engelska)
Opponent
Handledare
Tillgänglig från: 2010-11-03 Skapad: 2010-10-11 Senast uppdaterad: 2010-10-26Bibliografiskt granskad

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Av författaren/redaktören
Vigren, ErikHamberg, MathiasZhaunerchyk, VitaliLarsson, MatsThomas, Richard D.af Ugglas, MagnusKashperka, IrynaGeppert, Wolf D.
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