| 1. |
- Ehlerding, A., et al.
(author)
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The dissociative recombination of fluorocarbon ions III : CF2+ and CF3
- 2006
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In: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 39:4, s. 805-812
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Journal article (peer-reviewed)abstract
- Cross sections and branching ratios are presented for the dissociative recombination of the CF2+ and C-3(+) ions with electrons. It is found that the channel producing CF + F is dominant for the reaction with CF2+ and the production of CF2 + F is dominant for the reaction with CF3+. The cross sections for these two ions are very similar.
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| 2. |
- Novotny, O, et al.
(author)
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The dissociative recombination of fluorocarbon ions : II. CF
- 2005
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In: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 38:10, s. 1471-1482
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Journal article (peer-reviewed)abstract
- The dissociative recombination and excitation of CF+ have been measured at the ASTRID and CRYRING storage rings. Though examination of the available potential energy curves would suggest that the recombination rate would be large for this ion, in fact a rate constant of 5.2 +/- 1.0 x 10(-8) (T-e/300)(-0.8) cm(3) s(-1) was found. The recombination cross section at low energies falls off to a minimum at 0.5 eV centre-of-mass collision energy but exhibits resonances at energies above this. The dissociative excitation cross section leading to C+ + F was also measured and this displays an onset beginning at about 7 eV.
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| 3. |
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| 4. |
- Viggiano, A. A., et al.
(author)
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Rate constants and branching ratios for the dissociative recombination of CO2
- 2005
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In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 122:22, s. 226101-
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Journal article (peer-reviewed)abstract
- The calculation of rate constants and branching ratios was carried out to study the dissociative recombination of CO2+. The recombination of CO2+ is significant in the atmospheres of Venus and Mars. Rate constants and cross sections were studied by ramping the electron beam around a center-of-mass energy of 0 eV. The results of the study confirms that all the recombination of CO2+ results in a simple bondbreaking to form CO plus O. The rate constants show good agreement with measurements at 300 K and the electron energy dependence is identical to storage ring results.
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| 5. |
- Andersson, Pontus, 1971, et al.
(author)
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Radiative lifetimes of metastable states of negative ions
- 2006
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In: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622 .- 2469-9926 .- 2469-9934. ; 73, s. 032705-
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Journal article (peer-reviewed)abstract
- We present a technique for measuring the radiative lifetimes of metastable states of negative ions that involves the use of a heavy-ion storage ring. The method has been applied to investigate the radiative decay of the np(3) P-2(1/2) levels of Te-(n=5) and Se-(n=4) and the 3p(3) D-2 state of Si- for which the J=3/2 and 5/2 levels were unresolved. All of these states are metastable and decay primarily by emission of E2 and M1 radiation. Multi Configuration Dirac-Hartree-Fock calculations of rates for the transitions in Te- and Se- yielded lifetimes of 0.45 s and 4.7 s, respectively. The measured values agree well with these predicted values. In the case of the D-2 state of Si-, however, our measurement was only able to set a lower limit on the lifetime. The upper limit of the lifetime that can be measured with our apparatus is set by how long the ions can be stored in the ring, a limit determined by the rate of collisional detachment. Our lower limit of 1 min for the lifetime of the D-2 state is consistent with both the calculated lifetimes of 162 s for the D-2(3/2) level and 27.3 h for the D-2(5/2) level reported by O'Malley and Beck and 14.5 h and 12.5 h, respectively, from our Breit-Pauli calculations.
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| 6. |
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| 7. |
- Collins, G F, et al.
(author)
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Electron-impact fragmentation of Cl-2(-)
- 2005
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In: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 72:4, s. 042708-
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Journal article (peer-reviewed)abstract
- A merged beam technique has been used to investigate the fragmentation of the Cl-2(-) ion in collisions with electrons over an energy range of 0-200 eV. We have measured absolute cross sections for detachment, detachment plus dissociation and dissociation processes. Over the energy range studied, the dominant breakup mechanism is dissociation. Dissociation is relatively enhanced in the e(-)+Cl-2(-) collision system due to the suppression of the normally dominant detachment process, as a result of the large difference between the equilibrium internuclear distances of the Cl-2 and Cl-2(-) ground state potential curves. A prominent structure is observed just above the threshold in the Cl-+Cl+e(-) dissociation channel. It is proposed that the structure is a resonance associated with production and rapid decay of an excited state of the doubly charged Cl-2(-) ion. A plausible mechanism for production of the di-anionic state based on an excitation plus capture process is suggested.
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| 8. |
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| 9. |
- Montaigne, Helen, et al.
(author)
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Dissociative recombination of the thioformyl (HCS+) and carbonyl sulfide (OCS+) cations
- 2005
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In: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 631:1, s. 653-659
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Journal article (peer-reviewed)abstract
- Branching ratios and absolute cross sections have been measured for the dissociative recombination of HCS+ and OCS+ at the CRYRING ion storage ring. In the case of OCS+, the channel leading to CO + S ( 83%) dominates, whereas the other exoergic pathways leading to CS + O (14%) and C + SO (3%) are of lesser importance. In the case of HCS+, fracture of the C - S bond is predominant (81%), with the production of H + CS accounting for the remainder (19%). The cross section of the reaction could be fitted by the expressions sigma = 1.41 x 10(-15)E(eV)(-1.11) and 4.47 x 10(-16)E(eV) (-1.14) cm(2) for HCS+ and OCS+, respectively. The derived energy dependences of the thermal reaction rate coefficients can be fitted by k(T) 9.7 x 10(-7)(T/300)(-0.57) and 3.5 x 10(-7)(T/300)(-0.62) cm(3) s(-1) for HCS+ and OCS+, respectively. We use these data to perform model calculations on the HCS+/CS abundance ratio in dark clouds and find that the models using the UMIST and Ohio State University databases have even more difficulty in accounting for the large observed ratio.
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| 10. |
- Öjekull, Jenny, 1973, et al.
(author)
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Dissociative recombination of ammonia clusters studied by storage ring experiments
- 2006
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In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 125:19, s. 194306-
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Journal article (peer-reviewed)abstract
- Dissociative recombination of ammonia cluster ions with free electrons has been studied at the heavy-ion storage ring CRYRING (Manne Siegbahn Laboratory, Stockholm University). The absolute cross sections for dissociative recombination of H+(NH3)(2), H+(NH3)(3), D+(ND3)(2), and D+(ND3)(3) in the collision energy range of 0.001-27 eV are reported, and thermal rate coefficients for the temperature interval from 10 to 1000 K are calculated from the experimental data and compared with earlier results. The fragmentation patterns for the two ions H+(NH3)(2) and D+(ND3)(2) show no clear isotope effect. Dissociative recombination of X+(NX3)(2) (X=H or D) is dominated by the product channels 2NX(3)+X [0.95 +/- 0.02 for H+(NH3)(2) and 1.00 +/- 0.02 for D+(ND3)(2)]. Dissociative recombination of D+(ND3)(3) is dominated by the channels yielding three N-containing fragments (0.95 +/- 0.05).
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| 11. |
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| 12. |
- Fedosseev, V. N., et al.
(author)
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ISOLDE RILIS : New beams, new facilities
- 2008
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In: Nuclear Instruments and Methods in Physics Research Section B. - : Elsevier BV. - 0168-583X .- 1872-9584. ; 266:19-20, s. 4378-4382
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Journal article (peer-reviewed)abstract
- The resonance ionization laser ion source (RILIS) at the ISOLDE on-line isotope separator is based on the selective excitation of atomic transitions by tunable laser radiation. New ion beams have been produced with RILIS in recent years: Sb, Sc, Dy, Au, Hg and Po. In total, isotopes of 26 different elements have been selectively laser-ionized and separated at ISOLDE. In order to facilitate the work on development of atomic ionization schemes an off-line laser laboratory has been established at CERN. Operating independently of the on-line RI LIS setup, this laboratory will be capable of providing extensive data on atomic transitions, in particular between highly excited and auto-ionizing atomic states, which are required for the improvement of the RILIS efficiency. Additionally, the program gram of upgrading the on-line RI LIS system by the implementation of solid state lasers will be presented.
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| 13. |
- Geppert, W. D., et al.
(author)
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Dissociative recombination of CD3OD2
- 2005
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In: Proceedings of the International Astronomical Union. - 1743-9213 .- 1743-9221. ; 1, s. 117-124
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Journal article (peer-reviewed)abstract
- The branching ratios of the different reaction pathways and the overall rate of the dissociative recombination of CD3OD2 + were measured at the CRYRING storage ring located at the Manne Siegbahn Laboratory in Stockholm, Sweden. A preliminary analysis of the data yielded that formation of methanol accounts for only 6±2% of the total reaction rate. Largely, dissociative recombination of CD3OD 2 + involves fragmentation of the C-O bond, the major process being the three-body break-up forming CD3, OD and D (branching ratio 0.59). A non-negligible formation of interstellar methanol by the previously proposed mechanism is therefore very unlikely.
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| 14. |
- Geppert, W.D., et al.
(author)
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Dissociative recombination of protonated methanol
- 2006
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In: Faraday discussions. - Cambridge : Royal Society of Chemistry (RSC). - 1359-6640 .- 1364-5498. ; 133, s. 177-190
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Journal article (peer-reviewed)abstract
- The branching ratios of the different reaction pathways and the overall rate coefficients of the dissociative recombination reactions of CH3OH2+ and CD3OD2+ have been measured at the CRYRING storage ring located in Stockholm, Sweden. Analysis of the data yielded the result that formation of methanol or deuterated methanol accounted for only 3 and 6% of the total rate in CH3OH2+ and CD3OD2+, respectively. Dissociative recombination of both isotopomeres mainly involves fragmentation of the C - O bond, the major process being the three-body break-up forming CH3, OH and H (CD3, OD and D). The overall cross sections are best fitted by sigma = 1.2 +/- 0.1 x 10(-15) E-1.15 +/- 0.02 cm(2) and sigma = 9.6 +/- 0.9 x 10(-16) E-1.20 +/- 0.02 cm(2) for CH3OH2+ and CD3OD2+, respectively. From these values thermal reaction rate coefficients of k(T) = 8.9 +/- 0.9 x 10(-7) (T/300) (- 0.59 +/- 0.02) cm(3) s(-1) (CH3OH2+) and k( T) = 9.1 +/- 0.9 x 10(-7) (T/ 300) (- 0.63 +/- 0.02) cm(3) s(-1)(CD3OD2+) can be calculated. A non-negligible formation of interstellar methanol by the previously proposed mechanism via radiative association of CH3+ and H2O and subsequent dissociative recombination of the resulting CH3OH2+ ion to yield methanol and hydrogen atoms is therefore very unlikely.
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| 15. |
- Geppert, W. D., et al.
(author)
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Formation of biomolecule precursors in space
- 2007
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In: Journal of Physics, Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 88:1, s. 012068-
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Journal article (peer-reviewed)abstract
- Alcohols and nitriles not only play an important role as templates for synthesis of larger molecules in the interstellar medium and planetary atmospheres, but they can also be regarded as precursors for biomolecules. Alcohols can form carbohydrates through reaction with HCO and nitriles can be hydrolysed to amino acids in aqueous solutions, which is the final step of the well-known Strecker synthesis. Therefore the question of the pathways of formation of alcohols and nitriles and the efficiency and the product distribution of their subsequent degradation reactions in the above-mentioned astrophysical environments is of great interest. In both processes dissociative recombination reactions of protonated nitriles and alcohols may play a major role and are included in models of interstellar clouds and planetary atmospheres. However, the reaction rate coefficients and product branching ratios for the majority of these processes are so far still unknown, which adversely affects the quality of predictions of model calculations. In this Contribution, we therefore present branching ratios and rate constants of the dissociative recombination of protonated methanol (CH3OH 2), as well as protonated acetonitrile (CH3CNH +), acrylonitrile (C2H3CNH+) and cyanoacetylene (HC3NH+). The impact of the obtained new data on model calculations of abundances of important interstellar molecules in dark clouds is discussed.
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| 16. |
- Gylfason, Kristinn B., 1978-, et al.
(author)
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A packaged optical slot-waveguide ring resonator sensor array for multiplex assays in labs-on-chip
- 2009
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In: Proceedings of Conference, MicroTAS 2009 - The 13th International Conference on Miniaturized Systems for Chemistry and Life Sciences. - : Chemical and Biological Microsystems Society. - 9780979806421 ; , s. 2004-2006
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Conference paper (peer-reviewed)abstract
- We present the design, fabrication, and characterization of a packaged array of individually addressable slot-waveguide ring resonator sensors in a compact cartridge for sensitive, label-free, multiplex assays. The novel use of a dual surfaceenergy adhesive film enables simple generic packaging method for multiple sensors in a single cartridge. The use of optical slot-waveguides, and drift compensation by on-chip light splitting to reference sensors, gives the best refractive-index limit of detection reported for planar ring resonator sensors.
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| 17. |
- Hellberg, F, et al.
(author)
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Investigating the breakup dynamics of dihydrogen sulfide ions recombining with electrons
- 2005
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In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 122:22, s. 224314-
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Journal article (peer-reviewed)abstract
- This paper presents results concerning measurements of the dissociative recombination (DR) of dihydrogen sulfide ions. In combination with the ion storage ring CRYRING an imaging technique was used to investigate the breakup dynamics of the three-body channel in the DR of (SD2+)-S-32. The two energetically available product channels S(P-3)+2D(S-2) and S(D-1)+2D(S-2) were both populated, with a branching fraction of the ground-state channel of 0.6(0.1). Information about the angle between the two deuterium atoms upon dissociation was obtained together with information about how the available kinetic energy was distributed between the two light fragments. The recombination cross sections as functions of energy in the interval of 1 meV to 0.3 eV in the center-of-mass frame are presented for (SH2+)-S-34. The thermal rate coefficient for the DR of (SH2+)-S-34 was determined to be (4.8 +/- 1.0)x10(-7)(T/300)(-0.72 +/- 0.1) cm(3) s(-1) over this interval.
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| 18. |
- Kärrholm Peng, Fabian, 1980, et al.
(author)
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MODELLING INJECTOR FLOW INCLUDING CAVITATION EFFECTS FOR DIESEL APPLICATIONS
- 2007
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In: ASME Fluids Engineering Conference.
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Conference paper (peer-reviewed)abstract
- In this paper, cavitation and pressure parameters measuredin a model diesel injector are compared to data acquired by numericalsimulations using a new code developed for the Open-FOAM platform, which uses a barotropic equation of state togetherwith the homogeneous equilibrium assumption. It is aviscid code, allowing both compressible liquid and vapour tobe modelled. The mass flow and cavitation probabilities obtainedfrom the simulations are compared to data obtained inexperiments performed at AVL’s laboratories, in which the flowthrough an almost two-dimensional nozzle was examined. Theexperimental data used include pressure profiles and cavitationimages. The model proved to be able to predict cavitation probabilities,mass flows, and the occurrence of super-cavitation inthe channel. In addition, it proved to be stable in its dependencyon physical parameters, and grid independent.
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| 19. |
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| 20. |
- Kärrholm Peng, Fabian, 1980, et al.
(author)
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Three-Dimensional Simulation of Diesel Spray Ignition and Flame Lift-Off Using OpenFOAM and KIVA-3V CFD Codes
- 2008
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In: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191 .- 2688-3627.
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Journal article (peer-reviewed)abstract
- Three-dimensional simulations of ignition and combustion of a dieselspray were conducted. The primary goal of the work was to compare twodifferent CFD codes: OpenFOAM, an object-oriented C++ based code, andKIVA-3V. The spray is modelled by the Eulerian-Lagrangian approach inboth codes, with several common submodels. Some important sub-modelsimplemented include \emph{inter alia} aKelvin-Helmholtz/Rayleigh-Taylor (KH/RT) model for spray break-up, animproved spray collision model, and a Partially Stirred Reactor (PaSR)model for turbulence-chemistry interaction. Both CFD codes solve thechemical reaction equations in a fully coupled manner. A cubic-shaped Cartesianmesh was used in the KIVA-3V simulations, while a polyhedral meshincluding a combination of hexagonal and prism-shaped cells wasconstructed for the OpenFOAM computations.The effects of high EGR and ambient temperature on the ignition and flamelift-off processes of a diesel spray were investigated. Sandia experimentsconducted in a high-pressure and high-temperature constant-volume vessel werechosen for the simulations and validations. A single spray was injected intothe vessel, and EGR was mimicked by reducing the oxygen concentration. Thediesel reference fuel (n-heptane) was considered. For the study, a medium-sizemechanism involving 83 species and 338 reactions was employed. The mechanismwas validated using the CHEMKIN II package and the reaction rate constantswere adjusted on the basis of measurements of auto-ignition delays ofn-heptane/air mixtures in shock-tube experiments (with equivalence ratiosranging from 0.2 to 0.4 at 50 bar, and from 0.5 to 2.0 at 13.5 bar and 41.0bar), laminar flame speeds (1 atm and 3 atm), and flame structure inburner-stabilized premixed flames (1 atm).The simulations demonstrate that both CFD codes are capable of spray ignitionand combustion studies, though both show stronggrid-dependence. The numerical results show that the ignition delay,flame lift-off and combustion temperature of the spray are stronglyinfluenced by EGR and ambient gas temperature. These predictions arein agreement with measurements. Nevertheless, differences are observedbetween the results predicted by OpenFOAM and those from KIVA-3V, forexample, the flame predicted by the former is thinner and longer than that by thelatter, which requires further investigation.
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| 21. |
- Mosbach, S., et al.
(author)
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Dual injection homogeneous charge compression ignition engine simulation using a stochastic reactor model
- 2007
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In: International Journal of Engine Research. - 1468-0874. ; 8:1, s. 41-50
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Journal article (peer-reviewed)abstract
- Multiple direct injection (MDI) is a promising strategy to enable fast-response ignition control as well as expansion of the homogeneous charge compression ignition (HCCI) engine operating window, thus realizing substantial reductions of soot and NOx emissions. The present paper extends a zero-dimensional-probability-density-function-based stochastic reactor model (SRM) for HCCI engines in order to incorporate MDI and an improved turbulent mixing model. For this, a simplistic spray model featuring injection, penetration, and evaporation sub-models is formulated, and mixing is described by the Euclidean minimal spanning tree (EMST) sub-model accounting for localness in composition space. The model is applied to simulate a gasoline HCCI engine, and the in-cylinder pressure predictions for single and dual injection cases show a satisfactory agreement with measurements. From the parametric studies carried out it is demonstrated that, as compared with single injection, the additional second injection contributes to prolonged heat release and consequently helps to prevent knock, thereby extending the operating range on the high load side. Tracking the phase space trajectories of individual stochastic particles provides significant insight into the influence of local charge stratification owing to direct injection on HCCI combustion.
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| 22. |
- Schwellnus, F., et al.
(author)
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Study of low work function materials for hot cavity resonance ionization laser ion sources
- 2009
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In: Nuclear Instruments and Methods in Physics Research Section B. - : Elsevier BV. - 0168-583X .- 1872-9584. ; 267:10, s. 1856-1861
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Journal article (peer-reviewed)abstract
- The selectivity of a hot cavity resonance ionization laser ion source (RILIS) is most often limited by contributions from competing surface ionization of the hot walls of the ionization cavity. In this article we present investigations on the properties of designated high temperature, low work function materials regarding their performance and suitability as cavity material for RILIS. Tungsten test cavities, impregnated with a mixture of barium oxide and strontium oxide (BaOSrO on W), or alternatively gadolinium hexaboride (GdB6) were studied in comparison to a standard tungsten RILIS cavity as being routinely used for hot cavity laser ionization at ISOLDE. Measurement campaigns took place at the off-line mass separators at ISOLDE/CERN, Geneva and RISIKO/University of Mainz.
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| 23. |
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| 24. |
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| 25. |
- Österdahl, Fabian, et al.
(author)
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Position- and time-sensitive coincident detection of fragments from the dissociative recombination of O-2(+) using a single hexanode delay-line detector
- 2005
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In: DR2004. - BRISTOL : IOP PUBLISHING LTD. ; , s. 286-289
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Conference paper (other academic/artistic)abstract
- This contribution describes the use of the RoentDek hexanode delay line detector to detect fragments from the dissociative recombination of O-2(+) in an experiment at the ion storage ring CRYRING, Manne Siegbahn Laboratory, Stockholm. In this experiment, the fragments have a maximum time- and position-separation of 20ns and 40 mm, respectively. The position resolution obtained was 0.16mm (FWHM) on the 67 rum diameter detector. The time resolution obtained from the time-of-arrival difference between the product fragments was about 1 ns. The detector system handles event rates as large as 30 kHz. Techniques for the calibration of the absolute position of particles on the detector are discussed.
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