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Dissociative recombination of the deuterated acetaldehyde ion, CD3CDO+: product branching fractions, absolute cross sections and thermal rate coefficient
Stockholm University, Faculty of Science, Department of Physics.
Stockholm University, Faculty of Science, Department of Physics.
Stockholm University, Faculty of Science, Department of Physics.
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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.

Place, publisher, year, edition, pages
2007. Vol. 9, no 22, 2856-2861 p.
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:su:diva-43005DOI: 10.1039/B700649GISI: 000247349200020OAI: oai:DiVA.org:su-43005DiVA: diva2:352906
Available from: 2010-09-23 Created: 2010-09-23 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Dissociative recombination of organic molecular ions of relevance for interstellar clouds and Titan's upper atmosphere
Open this publication in new window or tab >>Dissociative recombination of organic molecular ions of relevance for interstellar clouds and Titan's upper atmosphere
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
Dissociative recombination, Astrochemistry
National Category
Physical Sciences
Research subject
Chemical Physics
Identifiers
urn:nbn:se:su:diva-43372 (URN)978-91-7447-133-5 (ISBN)
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
2. Spectroscopic study of titanium monohydride and storage ring experiments
Open this publication in new window or tab >>Spectroscopic study of titanium monohydride and storage ring experiments
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis describes two projects, spectroscopy of the astrophysically relevant molecule TiH and its isotopologue TiD, and the dissociative recombination (DR) reaction of astrophysically and atmospherically relevant molecules. Emphasis in the thesis is on the first project.

A series of laser aided spectroscopic studies of TiH/TiD has been carried out. A search for forbidden transitions in the (green) B-X band of TiH was performed. This was followed by a rather bitter fight for the analysis of the perturbed and congested B-X band of TiD, and this was finally rewarding. A substantial extension of a previously reported analysis of this band was performed. The new analysis includes transitions between higher vibrational levels never previously identified. This made it possible to report the first experimentally derived equilibrium constants for the TiH/TiD molecules. There is a need for such results for metal hydrides in the work of calculating the opacity of the atmospheres of cool M and L type stars.

The DR storage ring experiments have been carried out at the ion storage ring CRYRING in Stockholm. Measurements of the branching fractions and DR rate constants of molecular ions have been done. These results find use in the modeling of the chemistry in interstellar clouds as well as of atmospheres, like the one of Titan, one of the moons of Saturn, which was recently visited by the spacecraft Cassini.

Place, publisher, year, edition, pages
Stockholm: Fysikum, 2008. 72 p.
Keyword
TiH, TiD, transition metal hydride, dissociative recombination
National Category
Physical Chemistry
Research subject
Chemical Physics
Identifiers
urn:nbn:se:su:diva-7451 (URN)978-91-7155-619-6 (ISBN)
Public defence
2008-04-18, sal FA32, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 14:00
Opponent
Supervisors
Available from: 2008-03-27 Created: 2008-03-27 Last updated: 2010-10-21Bibliographically approved

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