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Hamberg M.,University of Stockholm | Zhaunerchyk V.,University of Stockholm | Zhaunerchyk V.,Radboud University Nijmegen | Vigren E.,University of Stockholm | And 13 more authors.
Astronomy and Astrophysics | Year: 2010

Aims. We determine branching fractions, cross sections and thermal rate constants for the dissociative recombination of CD3CDOD+ and CH3CH2OH2 + at the low relative kinetic energies encountered in the interstellar medium. Methods. The experiments were carried out by merging an ion and electron beam at the heavy ion storage ring CRYRING, Stockholm, Sweden. Results. Break-up of the CCO structure into three heavy fragments is not found for either of the ions. Instead the CCO structure is retained in 23 ± 3% of the DR reactions of CD3CDOD+ and 7 ± 3% in the DR of CH 3CH2OH2 +, whereas rupture into two heavy fragments occurs in 77 ± 3% and 93 ± 3% of the DR events of the respective ions. The measured cross sections were fitted between 1-200 meV yielding the following thermal rate constants and cross-section dependencies on the relative kinetic energy: σ(Ecm[eV]) = 1.7 ± 0.3 × 10-15 (Ecm[eV])-1.23 ± 0.02 cm2 and k(T) = 1.9 ± 0.4 × 10-6 (T/300) -0.73 ± 0.02 cm3 s-1 for CH 3CH2OH2 + as well as k(T) = 1.1 ± 0.4 × 10-6 (T/300)-0.74 ± 0.05 cm3 s-1 and σ(Ecm[eV]) = 9.2 ± 4 × 10-16 (Ecm[eV])-1.24 ± 0.05 cm2 for CD3CDOD+ © 2010 ESO. Source


Andersson P.U.,Gothenburg University | Ojekull J.,Gothenburg University | Pettersson J.B.C.,Gothenburg University | Markovic N.,Chalmers University of Technology | And 11 more authors.
Journal of Physical Chemistry Letters | Year: 2010

The internal energy distribution of ammonia formed in the dissociative recombination (DR) of NH4 + with electrons has been studied by an imaging technique at the ion storage ring CRYRING. The DR process resulted in the formation of NH3 + H (0.90 ± 0.01), with minor contributions from channels producing NH2 + H2 (0.05 ± 0.01) and NH2 + 2H (0.04 ± 0.02). The formed NH 3 molecules were highly internally excited, with a mean rovibrational energy of 3.3 ± 0.4 eV, which corresponds to 70% of the energy released in the neutralization process. The internal energy distribution was semiquantitatively reproduced by ab initio direct dynamics simulations, and the calculations suggested that the NH3 molecules are highly vibrationally excited while rotational excitation is limited. The high internal excitation and the translational energy of NH3 and H will influence their subsequent reactivity, an aspect that should be taken into account when developing detailed models of the interstellar medium and ammonia-containing plasmas. © 2010 American Chemical Society. Source


Hamberg M.,University of Stockholm | Vigren E.,University of Stockholm | Thomas R.D.,University of Stockholm | Zhaunerchyk V.,Radboud University Nijmegen | And 11 more authors.
EAS Publications Series | Year: 2011

We have investigated the dissociative recombination (DR) of the C 6D6 + and C6D7 + ions using the CRYRING heavy-ion storage ring at Stockholm University, Sweden. The dissociative recombination branching ratios were determined at minimal collision energy, showing that the DR of both ions was dominated by pathways keeping the carbon atoms together in one product. The absolute reaction cross sections for the titular ions are best fitted by σ(Ecm [eV]) = 1.3 ± 0.4 × 10-15 (Ecm [eV]) -1.19 ± 0.02 cm2 (C6D6 +) and σ(Ecm [eV]) = 1.1 ± 0.3 × 10-15(Ecm [eV])-1.33 ± 0.02 cm 2 (C6D7 +}) in the intervals 3-300 meV and 3-200 meV respectively. The thermal rate constants of the titular reactions are best described by: k(T) = 1.3 ± 0.4 × 10 -6(T/300)-0.69 ± 0.02 cm3s-1 for C6D6 +} and k(T) = 2.0 ± 0.6 × 10-6 (T/300)-0.83 ± 0.02 cm3s -1 for C6D6 +}. These expressions correlates well with earlier flowing afterglow studies on the same process. © EAS, EDP Sciences 2011. Source


Hamberg M.,University of Stockholm | Osterdahl F.,University of Stockholm | Thomas R.D.,University of Stockholm | Zhaunerchyk V.,University of Stockholm | And 8 more authors.
Astronomy and Astrophysics | Year: 2010

Aims. Determination of branching fractions, cross sections and thermal rate coefficients for the dissociative recombination of CD3OCD 2 + (0-0.3 eV) and (CD3)2OD + (0-0.2 eV) at the low relative kinetic energies encountered in the interstellar medium. Methods. The measurements were carried out using merged electron and ion beams at the CRYRING storage ring, Stockholm, Sweden. Results. For (CD3)2OD+ we have experimentally determined the branching fraction for ejection of a single hydrogen atom in the DR process to be maximally 7% whereas 49% of the reactions involve the break up of the COC chain into two heavy fragments and 44% ruptures both C-O bonds. The DR of CD3OCD2 + is dominated by fragmentation of the COC chain into two heavy fragments. The measured thermal rate constants and cross sections are k(T) = 1.7 ± 0.5 × 10-6(T/300 -0.77pm0.01 cm3 s-1, σ = 1.2 ± 0.4 × 10-15(Ecm[eV])-1.27±0.01 cm2 and k(T) = 1.7 ± 0.6 × 10-6(T/300) -0.70pm,0.02 cm3 s-1, σ = 1.7 ± 0.6 × 10-15(Ecm[eV])-1.20±0.02 cm2 for CD3OCD2 + and (CD 3)2OD+, respectively. © ESO, 2010. Source

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