| 1. |
- Gatchell, Michael, et al.
(författare)
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Commissioning of the DESIREE storage rings - a new facility for cold ion-ion collisions
- 2014
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Ingår i: XXVIII International Conference on Photonic, Electronic and Atomic Collisions (ICPEAC 2013). - : Institute of Physics (IOP). ; 488:1
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Konferensbidrag (refereegranskat)abstract
- We report on the ongoing commissioning of the Double ElectroStatic Ion Ring ExpEriment, DESIREE, at Stockholm University. Beams of atomic carbon anions (C-) and smaller carbon anion molecules (C-2(-), C-3(-), C-4(-) etc.) have been produced in a sputter ion source, accelerated to 10 keV or 20 keV, and stored successfully in the two electrostatic rings. The rings are enclosed in a common vacuum chamber cooled to below 13 Kelvin. The DESIREE facility allows for studies of internally relaxed single isolated atomic, molecular and cluster ions and for collision experiments between cat-and anions down to very low center-of-mass collision energies (meV scale). The total thermal load of the vacuum chamber at this temperature is measured to be 32 W. The decay rates of stored ion beams have two components: a non-exponential component caused by the space charge of the beam itself which dominates at early times and an exponential term from the neutralization of the beam in collisions with residual gas at later times. The residual gas limited storage lifetime of carbon anions in the symmetric ring is over seven minutes while the 1/e lifetime in the asymmetric ring is measured to be about 30 seconds. Although we aim to improve the storage in the second ring, the number of stored ions are now sufficient for many merged beams experiments with positive and negative ions requiring milliseconds to seconds ion storage.
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| 2. |
- Gatchell, Michael, et al.
(författare)
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First results from the Double ElectroStatic Ion-Ring ExpEriment, DESIREE
- 2014
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Ingår i: XXVIII International Conference on Photonic, Electronic and Atomic Collisions (ICPEAC 2013). - : Institute of Physics (IOP). ; 488
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Konferensbidrag (refereegranskat)abstract
- We have stored the first beams in one of the rings of the double electrostatic ion-storage ring, DESIREE at cryogenic and at room temperature conditions. At cryogenic operations the following parameters are found. Temperature; T= 13K, pressure; p <10(-13) mbar, initial number of stored ions; N > 10(7) and storage lifetime of a C-2(-) beam; tau = 450 S.
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| 3. |
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| 4. |
- Hamberg, Mathias, et al.
(författare)
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Experimental Studies of (HCO+)-C-13 Recombining with Electrons at Energies between 2-50 000 meV
- 2014
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 118:31, s. 6034-6049
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Tidskriftsartikel (refereegranskat)abstract
- An investigation into the dissociative recombination process for (HCO+)-C-13 using merged ion-electron beam methods has been performed at the heavy ion storage ring CRYRING, Stockholm, Sweden. We have measured the branching fractions of the different product channels at similar to 0 eV collision energy to be the following: CO + H 87 +/- 2%, OH + C 9 +/- 2%, and O + CH 4 +/- 2%. The formation of electronically excited CO in the dominant reaction channel has also been studied, and we report the following tentative branching fractions for the different CO product electronic states: CO(X (1)Sigma(+)) + H, 54 +/- 10%; CO(a (3)Pi) + H, 23 +/- 4%; and CO(a' (3)Sigma(+)) + H, 23 +/- 4%. The absolute cross section between similar to 2-50 000 meV was measured and showed resonance structures between 3 and 15 eV. The cross section was fitted in the energy range relevant to astrophysics, i.e., between 1 and 300 meV, and was found to follow the expression sigma = 1.3 +/- 0.3 X 10(-16) E-1.29 +/- 0.05 cm(2) and the corresponding thermal rate constant was determined to be k(T) = 2.0 +/- 0.4 X 10(-7)(T/300)(-0.79 +/- 0.05) cm(3) s(-1). Radioastronomical observations with the IRAM 30 m telescope of HCO+ toward the Red Rectangle yielded an upper column density limit of 4 X 10(11) cm(-2) of HCO+ at the 1 sigma level in that object, indicating that previous claims that the dissociative recombination of HCO+ plays an important role in the production of excited CO molecules emitting the observed Cameron bands in that object are not supported.
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| 5. |
- Hamberg, Mathias, et al.
(författare)
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Experimental studies of the dissociative recombination for CD3CDOD+ and CH3CH2OH2
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Aims: Determination of 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 CH3CH2OH2+, 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 cm3s−1 for CH3CH2OH2+ as well as k(T) = 1.1 ± 0.4 × 10−6(T/300)−0.74±0.05 cm3s−1 and σ(Ecm[eV]) = 9.2 ± 4 × 10−16(Ecm[eV])−1.24±0.05 cm2 for CD3CDOD+.
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| 6. |
- Hamberg, Mathias, et al.
(författare)
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Experimental studies of the dissociative recombination processes for the dimethyl ether ions CD3OCD2+ and (CD3)2OD
- 2010
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 514, s. A83-
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Tidskriftsartikel (refereegranskat)abstract
- Aims: Determination of branching fractions, cross sections and thermal rate coefficients for the dissociative recombination of CD3OCD2+ (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)−0.77±0.01 cm3s−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)−0.70±0.02 cm3s−1,σ= 1.7 ± 0.6 × 10−15(Ecm[eV])−1.20±0.02 cm2 for CD3OCD2+ and (CD3)2OD+, respectively.
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| 7. |
- Hamberg, Mathias, et al.
(författare)
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Experimental studies on the dissociative recombination of H13CO+ with electrons at energies between 2 – 50 000 meV
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Determination of dissociative recombination processes of H13CO+ using merged ion-electron beam methods has been performed at the heavy storage ring CRYRING, Stockholm, Sweden. We have measured the branching fractions at ~0 eV as: CO+H 87±2%, OH+C 9±2% and O+CH 4±2%. The channels leading to CO+H have the following branching fractions between the accessible electronic states of CO(X1S+)+H 46±3%, CO(a3Pg)+H 20±1% and CO(a’3S+)+H 34±3% respectively. The reaction cross section was fitted between 1-300 meV and followed the expression σ = 1.2±0.25×10-16 E-1.32±0.02 cm2 and the corresponding thermal rate constant was determined to k(T) = 2.0±0.4×10−7(T/300)−0.82±0.02 cm3s−1. The cross sections between ~2-50 000 meV were investigated showing resonant structures between 3-15 eV.
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| 8. |
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| 9. |
- Orbán, Istvan, et al.
(författare)
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A new method for detecting the contribution of high Rydberg states to electron-ion recombination
- 2007
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Ingår i: Journal of Physics, Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 58:299, s. 299-302
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Tidskriftsartikel (refereegranskat)abstract
- A position sensitive detector for measuring field ionized electrons in the fringe field of a dipole magnet is presented. The detector provides a means to study, in a state selective fashion, recombination into high Rydberg states and offers a new method to investigate recombination enhancement effects. Several experimental considerations and possibilities are discussed in the text.
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| 10. |
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