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Dissociative recombination of organic molecular ions of relevance for interstellar clouds and Titan's upper atmosphere
Stockholm University, Faculty of Science, Department of Physics.
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
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.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University , 2010. , 70 p.
Keyword [en]
Dissociative recombination, Astrochemistry
National Category
Physical Sciences
Research subject
Chemical Physics
Identifiers
URN: urn:nbn:se:su:diva-43372ISBN: 978-91-7447-133-5 (print)OAI: oai:DiVA.org:su-43372DiVA: diva2:356132
Public defence
2010-11-26, sal FB42, AlbaNova Universitetscentrum, Roslagstullsbacken 21, Stockholm, 10:00 (English)
Opponent
Supervisors
Available from: 2010-11-03 Created: 2010-10-11 Last updated: 2010-10-26Bibliographically approved
List of papers
1. Dissociative recombination of fully deuterated protonated acetonitrile, CD3CND+: Product branching fractions, absolute cross section and thermal rate coefficient
Open this publication in new window or tab >>Dissociative recombination of fully deuterated protonated acetonitrile, CD3CND+: Product branching fractions, absolute cross section and thermal rate coefficient
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2008 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 10, no 27, 4014-4019 p.Article in journal (Refereed) Published
Abstract [en]

The dissociative recombination of fully deuterated protonated acetonitrile, CD3CND+, has been investigated at the CRYRING heavy ion storage ring, located at the Manne Siegbahn Laboratory, Stockholm, Sweden. Branching fractions were measured at similar to 0 eV relative collision energy between the ions and the electrons and in 65% of the DR events there was no rupture of bonds between heavy atoms. In the remaining 35%, one of the bonds between the heavy atoms was broken. The DR cross-section was measured between similar to 0 eV and 1 eV relative collision energy. In the energy region between 1 meV and 0.1 eV the cross section data were best fitted by the expression sigma = 7.37 x 10(-16) (E/eV)(-1.23) cm(2), whereas sigma = 4.12 x 10(-16) (E/eV)(-1.46) cm(2) was the best fit for the energy region between 0.1 and 1.0 eV. From the cross section a thermal rate coefficient of alpha(T) = 8.13 x 10(-7) (T/300)(-0.69) cm(3) s(-1) was deduced.

National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:su:diva-43002 (URN)10.1039/b801566j (DOI)000257425100006 ()
Available from: 2010-09-23 Created: 2010-09-23 Last updated: 2017-12-12Bibliographically approved
2. The Dissociative Recombination of Protonated Acrylonitrile, CH2CHCNH+, with implications for the Nitrile Chemistry in Dark Molecular Clouds and the Upper Atmosphere of Titan
Open this publication in new window or tab >>The Dissociative Recombination of Protonated Acrylonitrile, CH2CHCNH+, with implications for the Nitrile Chemistry in Dark Molecular Clouds and the Upper Atmosphere of Titan
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2009 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 695, no 1, 317-324 p.Article in journal (Refereed) Published
Abstract [en]

Measurements on the dissociative recombination (DR) of protonated acrylonitrile, CH2CHCNH+, have been performed at the heavy ion storage ring CRYRING located in the Manne Siegbahn Laboratory in Stockholm, Sweden. It has been found that at similar to 2meV relative kinetic energy about 50% of the DR events involve only ruptures of X-Hbonds (where X = C or N) while the rest leads to the production of a pair of fragments each containing two heavy atoms (alongside H and/or H-2). The absolute DR cross section has been investigated for relative kinetic energies ranging from similar to 1 meV to 1 eV. The thermal rate coefficient has been determined to follow the expression k(T) = 1.78 x 10(-6) (T/300)(-0.80) cm(3) s(-1) for electron temperatures ranging from similar to 10 to 1000 K. Gas-phase models of the nitrile chemistry in the dark molecular cloud TMC-1 have been run and results are compared with observations. Also, implications of the present results for the nitrile chemistry of Titan's upper atmosphere are discussed.

Keyword
ISM: clouds, ISM: molecules, methods: laboratory, molecular processes
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:su:diva-43004 (URN)10.1088/0004-637X/695/1/317 (DOI)000264779500027 ()
Available from: 2010-09-23 Created: 2010-09-23 Last updated: 2017-12-12Bibliographically approved
3. Dissociative Recombination of Protonated Propionitrile, CH3CH2CNH+: Implications for Titan's Upper Atmosphere
Open this publication in new window or tab >>Dissociative Recombination of Protonated Propionitrile, CH3CH2CNH+: Implications for Titan's Upper Atmosphere
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2010 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 722, no 1, 847-850 p.Article in journal (Refereed) Published
Abstract [en]

The dissociative recombination of protonated propionitrile, CH3CH2CNH+, has been investigated at the heavy ion storage ring, CRYRING, at the Manne Siegbahn Laboratory, Stockholm University, Sweden. The thermal rate coefficient has been deduced to follow k(T) = (1.5 ± 0.2) × 10–6 (T/300)–0.76 ± 0.02 cm3 s–1 for electron temperatures ranging from ~10 to ~1000 K. Measurements of the branching fractions were performed at ~0 eV relative kinetic energy. It has been found that in 43% ± 2% of the reactions the four heavy atoms remain in the same product fragment. An equal portion of the reactions leads to products where one of the heavy atoms is split off from the other three and 14% ± 1% result in a breakup into two heavy fragments containing two heavy atoms each. We discuss the significance of the data to Titan's upper atmosphere.

Keyword
methods: laboratory, molecular processes
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:su:diva-43010 (URN)10.1088/0004-637X/722/1/847 (DOI)000282908900069 ()
Available from: 2010-09-23 Created: 2010-09-23 Last updated: 2017-12-12Bibliographically approved
4. Dissociative recombination of the deuterated acetaldehyde ion, CD3CDO+: product branching fractions, absolute cross sections and thermal rate coefficient
Open this publication in new window or tab >>Dissociative recombination of the deuterated acetaldehyde ion, CD3CDO+: product branching fractions, absolute cross sections and thermal rate coefficient
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2007 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 9, no 22, 2856-2861 p.Article in journal (Refereed) Published
Abstract [en]

Dissociative recombination of the deuterated acetaldehyde ion CD3CDO+ has been studied at the heavy-ion storage ring CRYRING, located at the Manne Siegbahn Laboratory, Stockholm, Sweden. Product branching fractions together with absolute DR cross-sections were measured. The branching fractions were determined at a relative collision energy between the ions and the electrons of 0 eV. With a probability of 34% the DR events resulted in no ruptures of bonds between heavy atoms (i.e. no breakage of the C–C bond or the CO bond). In the remaining 66% of the events one of the bonds between the heavy atoms was broken. The energy-dependent cross-section for the DR reaction was measured between 0 and 1 eV relative kinetic energy. In the energy region between 1 meV and 0.2 eV the absolute cross section could be fitted by the expression σ(E) = 6.8 × 10−16E−1.28 cm2, whereas in the energy interval between 0.2 and 1 eV the data were best fitted by σ(E) = 4.1 × 10−16E−1.60 cm2. From these cross section data the thermal rate coefficient (as a function of the electron temperature), α(T) = 9.2 × 10−7 (T/300)−0.72 cm3 s−1 was obtained.

National Category
Natural Sciences
Identifiers
urn:nbn:se:su:diva-43005 (URN)10.1039/B700649G (DOI)000247349200020 ()
Available from: 2010-09-23 Created: 2010-09-23 Last updated: 2017-12-12Bibliographically approved
5. Dissociative recombination of the acetaldehyde cation, CH3CHO+
Open this publication in new window or tab >>Dissociative recombination of the acetaldehyde cation, CH3CHO+
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2010 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 12, no 37, 11670-11673 p.Article in journal (Refereed) Published
Abstract [en]

The dissociative recombination of the acetaldehyde cation, CH3CHO+, has been investigated at the heavy ion storage ring CRYRING at the Manne Siegbahn Laboratory in Stockholm, Sweden. The dependence of the absolute cross section of the reaction on the relative kinetic energy has been determined and a thermal rate coefficient of k(T) = (1.5 +/- 0.2) x 10(-6) (T/300)(-0.70 +/- 0.02) cm(3) s(-1) has been deduced, which is valid for electron temperatures between similar to 10 and 1000 K. The branching fractions of the reaction were studied at similar to 0 eV relative kinetic energy and we found that breaking one of the bonds between two of the heavy atoms occurs in 72 +/- 2% of the reactions. In the remaining events the three heavy atoms stay in the same product fragment. While the branching fractions are fairly similar to the results from an earlier investigation into the dissociative recombination of the fully deuterated acetaldehyde cation, CD3CDO+, the thermal rate coefficient is somewhat larger for CH3CHO+. Astrochemical implications of the results are discussed.

National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:su:diva-43008 (URN)10.1039/c003857a (DOI)000281726800055 ()
Available from: 2010-09-23 Created: 2010-09-23 Last updated: 2017-12-12Bibliographically approved
6. Dissociative Recombination of Protonated Formic Acid: Implications for Molecular Cloud and Cometary Chemistry
Open this publication in new window or tab >>Dissociative Recombination of Protonated Formic Acid: Implications for Molecular Cloud and Cometary Chemistry
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2010 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 709, no 2, 1429-1434 p.Article in journal (Refereed) 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.

Keyword
astrochemistry; molecular processes
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:su:diva-43009 (URN)10.1088/0004-637X/709/2/1429 (DOI)000273579800071 ()
Available from: 2010-09-23 Created: 2010-09-23 Last updated: 2017-12-12Bibliographically approved

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