| 1. |
- Yang, B., et al.
(författare)
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Exploring high-energy doubly excited states of NH by dissociative recombination of NH
- 2014
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Ingår i: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 47:3, s. 035201-
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated electron capture by NH+ resulting in dissociative recombination (DR). The impact energies studied of similar to 4-12 eV extend over the range below the two lowest predicted NH+ dissociative states in the Franck-Condon (FC) region of the ion. Our focus has been on the final state populations of the resulting N and H atoms. The neutral DR fragments are detected downstream of a merged electron and ion beam interaction zone in the TSR storage ring, which is located at the Max Planck Institute for Nuclear Physics in Heidelberg, Germany. Transverse fragment distances were measured on a recently developed high count-rate imaging detector. The distance distributions enabled a detailed tracking of the final state populations as a function of the electron collision energy. These can be correlated with doubly excited neutral states in the FC region of the ion. At low electron energy of similar to 5 eV, the atomic product final levels are nitrogen Rydberg states together with ground-state hydrogen. In a small electron energy interval near 7 eV, a significant part of the final state population forms hydrogen Rydberg atoms with nitrogen atoms in the first excited (D-2) term, showing the effect of Rydberg doubly excited states below the predicted 2(2)Pi ionic potential. The distance distributions above similar to 10 eV are compatible with nitrogen Rydberg states correlating to the doubly excited Rydberg state manifold below the ionic 2(4) Sigma(-) level.
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| 2. |
- Wakelam, V., et al.
(författare)
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The 2014 KIDA Network for Interstellar Chemistry
- 2015
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Ingår i: Astrophysical Journal Supplement Series. - : American Astronomical Society. - 0067-0049 .- 1538-4365. ; 217:2
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Tidskriftsartikel (refereegranskat)abstract
- Chemical models used to study the chemical composition of the gas and the ices in the interstellar medium are based on a network of chemical reactions and associated rate coefficients. These reactions and rate coefficients are partially compiled from data in the literature, when available. We present in this paper kida.uva.2014, a new updated version of the kida.uva public gas-phase network first released in 2012. In addition to a description of the many specific updates, we illustrate changes in the predicted abundances of molecules for cold dense cloud conditions as compared with the results of the previous version of our network, kida.uva.2011.
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| 3. |
- Novotny, O., et al.
(författare)
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DISSOCIATIVE RECOMBINATION MEASUREMENTS OF HCl+ USING AN ION STORAGE RING
- 2013
-
Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 777:1, s. 54-
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Tidskriftsartikel (refereegranskat)abstract
- We have measured dissociative recombination (DR) of HCl+ with electrons using a merged beams configuration at the TSR heavy-ion storage ring located at the Max Planck Institute for Nuclear Physics in Heidelberg, Germany. We present the measured absolute merged beams recombination rate coefficient for collision energies from 0 to 4.5 eV. We have also developed a new method for deriving the cross section from the measurements. Our approach does not suffer from approximations made by previously used methods. The cross section was transformed to a plasma rate coefficient for the electron temperature range from T = 10 to 5000 K. We show that the previously used HCl+ DR data underestimate the plasma rate coefficient by a factor of 1.5 at T = 10 K and overestimate it by a factor of three at T = 300 K. We also find that the new data may partly explain existing discrepancies between observed abundances of chlorine-bearing molecules and their astrochemical models.
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| 4. |
- Novotný, O., et al.
(författare)
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DISSOCIATIVE RECOMBINATION MEASUREMENTS OF NH+ USING AN ION STORAGE RING
- 2014
-
Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 792:2
-
Tidskriftsartikel (refereegranskat)abstract
- We have investigated dissociative recombination (DR) of NH+ with electrons using a merged beams configuration at the TSR heavy-ion storage ring located at the Max Planck Institute for Nuclear Physics in Heidelberg, Germany. We present our measured absolute merged-beams recombination rate coefficient for collision energies from 0 to 12 eV. From these data, we have extracted a cross section, which we have transformed to a plasma rate coefficient for the collisional plasma temperature range from T-p1 = 10 to 18,000 K. We show that the NH+ DR rate coefficient data in current astrochemical models are underestimated by up to a factor of approximately nine. Our new data will result in predicted NH+ abundances lower than those calculated by present models. This is in agreement with the sensitivity limits of all observations attempting to detect NH+ in interstellar clouds.
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| 5. |
- Wakelam, V., et al.
(författare)
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A KINETIC DATABASE FOR ASTROCHEMISTRY (KIDA)
- 2012
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Ingår i: Astrophysical Journal Supplement Series. - : American Astronomical Society. - 0067-0049 .- 1538-4365. ; 199:1, s. 21-
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Tidskriftsartikel (refereegranskat)abstract
- We present a novel chemical database for gas-phase astrochemistry. Named the KInetic Database for Astrochemistry (KIDA), this database consists of gas-phase reactions with rate coefficients and uncertainties that will be vetted to the greatest extent possible. Submissions of measured and calculated rate coefficients are welcome, and will be studied by experts before inclusion into the database. Besides providing kinetic information for the interstellar medium, KIDA is planned to contain such data for planetary atmospheres and for circumstellar envelopes. Each year, a subset of the reactions in the database (kida.uva) will be provided as a network for the simulation of the chemistry of dense interstellar clouds with temperatures between 10 K and 300 K. We also provide a code, named Nahoon, to study the time-dependent gas-phase chemistry of zero-dimensional and one-dimensional interstellar sources.
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| 6. |
- Gatchell, Michael, et al.
(författare)
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Commissioning of the DESIREE storage rings - a new facility for cold ion-ion collisions
- 2014
-
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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| 7. |
- Hartman, Henrik, et al.
(författare)
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First storage of ion beams in the Double Electrostatic Ion-Ring Experiment : DESIREE
- 2013
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Ingår i: Review of Scientific Instruments. - : American Institute of Physics (AIP). - 0034-6748 .- 1089-7623. ; 84:5
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Tidskriftsartikel (refereegranskat)abstract
- We report on the first storage of ion beams in the Double ElectroStatic Ion Ring ExpEriment, DESIREE, at Stockholm University. We have produced beams of atomic carbon anions and small carbon anion molecules (Cn-, n = 1, 2, 3, 4) in a sputter ion source. The ion beams were accelerated to 10 keV kinetic energy and stored in an electrostatic ion storage ring enclosed in a vacuum chamber at 13 K. For 10 keV C2- molecular anions we measure the residual-gas limited beam storage lifetime to be 448 s +/- 18 s with two independent detector systems. Using the measured storage lifetimes we estimate that the residual gas pressure is in the 10-14 mbar range. When high current ion beams are injected, the number of stored particles does not follow a single exponential decay law as would be expected for stored particles lost solely due to electron detachment in collision with the residual-gas. Instead, we observe a faster initial decay rate, which we ascribe to the effect of the space charge of the ion beam on the storage capacity.
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| 8. |
- Novotny, O., et al.
(författare)
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Dissociative Recombination Measurements of Chloronium Ions (D2Cl+) Using an Ion Storage Ring
- 2018
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 862:2
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Tidskriftsartikel (refereegranskat)abstract
- We report our plasma rate coefficient and branching ratio measurements for dissociative recombination (DR) of D2Cl+ with electrons. The studies were performed in a merged-beams configuration using the TSR heavy-ion storage ring located at the Max Planck Institute for Nuclear Physics in Heidelberg, Germany. Starting with our absolute merged-beams recombination rate coefficient at a collision energy of approximate to 0 eV, we have extracted the cross section and produced a plasma rate coefficient for a translational temperature of approximate to 8 K. Furthermore, extrapolating our cross-section results using the typical low-energy DR behavior, we have generated a plasma rate coefficient for translational temperatures from 5 to 500 K. We find good agreement between our extrapolated results and previous experimental DR studies on D2Cl+. Additionally, we have investigated the three fragmentation channels for DR of D2Cl+. Here we report on the dissociation geometry of the three-body fragmentation channel, the kinetic energy released for each of the three outgoing channels, the molecular internal excitation for the two outgoing channels that produce molecular fragments, and the fragmentation branching ratios for all three channels. Our results, in combination with those of other groups, indicate that any remaining uncertainties in the DR rate coefficient for H2Cl+ appear unlikely to explain the observed discrepancies between the inferred abundances of HCl and H2Cl+ in molecular clouds and predictions from astrochemical models.
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| 9. |
- Thomas, Richard D., et al.
(författare)
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DESIREE : Physics with cold stored ion beams
- 2015
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Ingår i: DR2013. - : EDP Sciences. ; 84, s. 01004-01004
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Konferensbidrag (refereegranskat)abstract
- Here we will briefly describe the commissioning of the Double ElectroStatic Ion Ring ExpEriment (DESIREE) facility at Stockholm University, Sweden. This device uses purely electrostatic focussing and deflection elements and allows ion beams of opposite charge to be confined under extreme high vacuum and cryogenic conditions in separate rings and then merged over a common straight section. This apparatus allows for studies of interactions between cations and anions at very low and well-defined centre-of-mass energies (down to a few meV) and at very low internal temperatures (down to a few K).
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| 10. |
- Tobie, G., et al.
(författare)
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Science goals and mission concept for the future exploration of Titan and Enceladus
- 2014
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Ingår i: Planetary and Space Science. - : Elsevier BV. - 0032-0633 .- 1873-5088. ; 104, s. 59-77
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Tidskriftsartikel (refereegranskat)abstract
- Saturn's moons, Titan and Enceladus, are two of the Solar System's most enigmatic bodies and are prime targets for future space exploration. Titan provides an analogue for many processes relevant to the Earth, more generally to outer Solar System bodies, and a growing host of newly discovered icy exoplanets. Processes represented include atmospheric dynamics, complex organic chemistry, meteorological cycles (with methane as a working fluid), astrobiology, surface liquids and lakes, geology, fluvial and aeolian erosion, and interactions with an external plasma environment. In addition, exploring Enceladus over multiple targeted flybys will give us a unique opportunity to further study the most active icy moon in our Solar System as revealed by Cassini and to analyse in situ its active plume with highly capable instrumentation addressing its complex chemistry and dynamics. Enceladus' plume likely represents the most accessible samples from an extra-terrestrial liquid water environment in the Solar system, which has far reaching implications for many areas of planetary and biological science. Titan with its massive atmosphere and Enceladus with its active plume are prime planetary objects in the Outer Solar System to perform in situ investigations. In the present paper, we describe the science goals and key measurements to be performed by a future exploration mission involving a Saturn-Titan orbiter and a Titan balloon, which was proposed to ESA in response to the call for definition of the science themes of the next Large-class mission in 2013. The mission scenario is built around three complementary science goals: (A) Titan as an Earth-like system; (B) Enceladus as an active cryovolcanic moon; and (C) Chemistry of Titan and Enceladus - clues for the origin of life. The proposed measurements would provide a step change in our understanding of planetary processes and evolution, with many orders of magnitude improvement in temporal, spatial, and chemical resolution over that which is possible with Cassini-Huygens. This mission concept builds upon the successes of Cassini-Huygens and takes advantage of previous mission heritage in both remote sensing and in situ measurement technologies. (C) 2014 Elsevier Ltd. All rights reserved.
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| 11. |
- Andersson, Patrik U, 1970, et al.
(författare)
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Formation of Highly Rovibrationally Excited Ammonia from Dissociative Recombination of NH4
- 2010
-
Ingår i: Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 1:17, s. 2519-2523
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Tidskriftsartikel (refereegranskat)abstract
- 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 NH3 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.
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| 12. |
- Fathi, Pantea, et al.
(författare)
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Experimental and theoretical investigations of the ion-neutral reaction of C2H2N+ with C2H6 and implications on chain elongation processes in Titan's atmosphere
- 2016
-
Ingår i: International Journal of Mass Spectrometry. - : Elsevier BV. - 1387-3806 .- 1873-2798. ; 411, s. 1-13
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Tidskriftsartikel (refereegranskat)abstract
- In this study we report theoretical and experimental evidence for the formation of ionic products by the ion-neutral reaction of C2H2N+ with C2H6. Our investigations consist of laboratory measurements using a guided ion beam mass spectrometer together with complementary ab initio quantum chemical computations, at the MP2/6-311++G(d,p) level of theory, in order to elucidate the energetics and geometries of the intermediates and transition states that are involved in the production of the observed product ions. This study also provides insights on the isomeric nature of the observed product ions, their formation pathways together with collision energy and pressure dependences. The experimental data agrees well with the predictions of the ab initio calculations. Despite data provides evidence for the occurrence of C2H5+ as the most salient product ion, the production of CH3+, C2H3+, C3H5+, C3H7+ and C2H4N+ is also evident. A reaction scheme was proposed to elucidate the mechanisms responsible for the formation of the observed product ions. These processes might be intermediate steps in the generation of long chain carbon and nitrogen-bearing compounds in Titan's ionosphere, the interstellar medium or circumstellar envelopes.
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| 13. |
- Fathi, Pantea, et al.
(författare)
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Ion-neutral reaction of C2H2N+ with CH4 : An experimental and theoretical study
- 2016
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Ingår i: Molecular Astrophysics. - : Elsevier BV. - 2405-6758 .- 2405-674X. ; 5, s. 9-22
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Tidskriftsartikel (refereegranskat)abstract
- The current study was undertaken to probe the ionic products of the ion-neutral reaction of C2H2N+ with CH4 using guided ion beam mass spectrometry (GIB-MS) in which the CH3+, C2H3+, HCNH+, C2H5+, C2H3N+ and C3H4N+ ions are identified as products. Theoretical calculations were performed to suggest reaction pathways leading to the detected products. These processes might be of relevance for the generation of long chain carbon-nitrogen bearing compounds in Titan's atmosphere, the interstellar medium or circumstellar envelopes.
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| 14. |
- Fathi, Pantea, et al.
(författare)
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Ion-neutral reaction of the C2H2N+ cation with C2H2 : An experimental and theoretical study
- 2016
-
Ingår i: Molecular Astrophysics. - : Elsevier BV. - 2405-6758 .- 2405-674X. ; 2, s. 1-11
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Tidskriftsartikel (refereegranskat)abstract
- The ion-neutral reactions of the C2H2N+ cation with C2H2 have been investigated using a Guided Ion Beam Mass Spectrometer (GIB-MS). The following ionic products were observed: CH3+, C2H2+, C2H3+, HNC+/HCN+, HCNH+, C3H+, C2N+, C3H3+, HCCN+ and C4H2N+. Theoretical calculations have been carried out to propose reaction pathways leading to the observed products. These processes are of relevance for the generation of long chain nitrogen-containing species and they may be of interest for the chemistry of Titan’s ionosphere or circumstellar envelopes.
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| 15. |
- Gatchell, Michael, et al.
(författare)
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First results from the Double ElectroStatic Ion-Ring ExpEriment, DESIREE
- 2014
-
Ingår i: XXVIII International Conference on Photonic, Electronic and Atomic Collisions (ICPEAC 2013). - : Institute of Physics (IOP). ; 488
-
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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| 16. |
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| 17. |
- 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
-
Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 118:31, s. 6034-6049
-
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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| 18. |
- 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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| 19. |
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| 20. |
- Kumar, S. S., et al.
(författare)
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PHOTODETACHMENT AS A DESTRUCTION MECHANISM FOR CN- AND C3N- ANIONS IN CIRCUMSTELLAR ENVELOPES
- 2013
-
Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 776:1, s. 25-
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Tidskriftsartikel (refereegranskat)abstract
- Absolute photodetachment cross sections of two anions of astrophysical importance CN- and C3N- were measured to be (1.18 +/- (0.03)(stat)(0.17)(sys)) x 10(-17) cm(2) and (1.43 +/- (0.14)(stat)(0.37)(sys)) x 10(-17) cm(2), respectively, at the ultraviolet (UV) wavelength of 266 nm (4.66 eV). These relatively large values of the cross sections imply that photodetachment can play a major role in the destruction mechanisms of these anions particularly in photon-dominated regions. We have therefore carried out model calculations using the newly measured cross sections to investigate the abundance of these molecular anions in the cirumstellar envelope of the carbon-rich star IRC+10216. The model predicts the relative importance of the various mechanisms of formation and destruction of these species in different regions of the envelope. UV photodetachment was found to be the major destruction mechanism for both CN- and C3N- anions in those regions of the envelope, where they occur in peak abundance. It was also found that photodetachment plays a crucial role in the degradation of these anions throughout the circumstellar envelope.
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| 21. |
- Rodriguez, Sébastien, et al.
(författare)
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Science goals and new mission concepts for future exploration of Titan's atmosphere, geology and habitability : titan POlar scout/orbitEr and in situ lake lander and DrONe explorer (POSEIDON)
- 2022
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Ingår i: Experimental astronomy. - : Springer Science and Business Media LLC. - 0922-6435 .- 1572-9508. ; 54:2-3, s. 911-973
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Tidskriftsartikel (refereegranskat)abstract
- In response to ESA’s “Voyage 2050” announcement of opportunity, we propose an ambitious L-class mission to explore one of the most exciting bodies in the Solar System, Saturn’s largest moon Titan. Titan, a “world with two oceans”, is an organic-rich body with interior-surface-atmosphere interactions that are comparable in complexity to the Earth. Titan is also one of the few places in the Solar System with habitability potential. Titan’s remarkable nature was only partly revealed by the Cassini-Huygens mission and still holds mysteries requiring a complete exploration using a variety of vehicles and instruments. The proposed mission concept POSEIDON (Titan POlar Scout/orbitEr and In situ lake lander DrONe explorer) would perform joint orbital and in situ investigations of Titan. It is designed to build on and exceed the scope and scientific/technological accomplishments of Cassini-Huygens, exploring Titan in ways that were not previously possible, in particular through full close-up and in situ coverage over long periods of time. In the proposed mission architecture, POSEIDON consists of two major elements: a spacecraft with a large set of instruments that would orbit Titan, preferably in a low-eccentricity polar orbit, and a suite of in situ investigation components, i.e. a lake lander, a “heavy” drone (possibly amphibious) and/or a fleet of mini-drones, dedicated to the exploration of the polar regions. The ideal arrival time at Titan would be slightly before the next northern Spring equinox (2039), as equinoxes are the most active periods to monitor still largely unknown atmospheric and surface seasonal changes. The exploration of Titan’s northern latitudes with an orbiter and in situ element(s) would be highly complementary in terms of timing (with possible mission timing overlap), locations, and science goals with the upcoming NASA New Frontiers Dragonfly mission that will provide in situ exploration of Titan’s equatorial regions, in the mid-2030s.
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| 22. |
- Thomas, Richard D., et al.
(författare)
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Dissociative Recombination of CH4
- 2013
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 117:39, s. 9999-10005
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Tidskriftsartikel (refereegranskat)abstract
- CH4+ is an important molecular ion in the astrochemistry of diffuse clouds, dense clouds, cometary comae, and planetary ionospheres However, the rate of one of the common destruction mechanisms for molecular ions in these regions, dissociative recombination (DR), is somewhat uncertain. Here, we present absolute measurements for the DR of CH4+ made using the heavy ion storage ring CRYRING hi Stockholm, Sweden. From our collision energy dependent cross sections, we infer a thermal rate constant of k(T-e) = 1.71(+/- 0.02) X 10(-6)(T-e/300)(-0.66(+/- 0.02)) cm(3) s(-1) over the region of electron temperatures 10 <= T-e <= 1000 K. At low collision energies, we have measured the branching fractions of the DR products to be CH4 (0.00 +/- 0.00); CH3 + H (0.18 +/- 0.03); CH2 + 2H (0.51 +/- 0.03); CH2 + H-2 (0.06 +/- 0.01); CH + H-2 + H (0.23 +/- 0.01); and CH + 2H(2) (0.02 +/- 0.01), indicating that two or more C-H bonds are broken in similar to 80% of all collisions.
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| 23. |
- Thomas, Richard D., et al.
(författare)
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Dissociative recombination of LiH2
- 2014
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 89:5, s. 050701-
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we report results regarding how LiH2+ fragments as a result of a low-energy collision with an electron (dissociative recombination), a reaction that contains only elements and particles created during the very first phase of the universe. The collision-energy-dependent reaction rate and cross sections show detailed structures, more so than predicted by theory, suggesting significant rovibrational coupling in the ion and a complex reaction surface. From the structure of the molecule, the reaction predominantly results in the formation of Li + H-2. However, 23% of the reaction flux leads to more interesting products, with 17% producing Li + 2H and 6% producing LiH + H. These last two channels break the strongest molecular bond in the system and, in the case of the latter channel, form a significantly weaker ionic bond. Possible reasons behind this interesting behavior are discussed, together with the interaction between the available reaction channels.
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| 24. |
- Thomas, R. D., et al.
(författare)
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Hot Water from Cold. The Dissociative Recombination of Water Cluster Ions
- 2010
-
Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 114:14, s. 4843-4846
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Tidskriftsartikel (refereegranskat)abstract
- Dissociative recombination of the Zundel cation D(5)O(2)(+) almost exclusively produces D + 2 D(2)O with a maximum kinetic energy release of 5.1 eV. An imaging technique is used to investigate the distribution of the available reaction energy among these products. Analysis shows that as much as 4 eV can be stored internally by the molecular fragments, with a preference for producing highly excited molecular fragments, and that the deuteron shows a nonrandom distribution of kinetic energies. A possible mechanism and the implications for these observations are addressed.
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| 25. |
- Tom, Brian A., et al.
(författare)
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Dissociative recombination of highly enriched para-H-3(+)
- 2009
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 130:3, s. 31101-
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Tidskriftsartikel (refereegranskat)abstract
- The determination of the dissociative recombination rate coefficient of H-3(+) has had a turbulent history, but both experiment and theory have recently converged to a common value. Despite this convergence, it has not been clear if there should be a difference between the rate coefficients for ortho-H-3(+) and para-H-3(+). A difference has been predicted theoretically and could conceivably impact the ortho:para ratio of H-3(+) in the diffuse interstellar medium, where H-3(+) has been widely observed. We present the results of an experiment at the CRYRING ion storage ring in which we investigated the dissociative recombination of highly enriched (similar to 83.6%) para-H-3(+) using a supersonic expansion source that produced ions with T-rot similar to 60-100 K. We observed an increase in the low energy recombination rate coefficient of the enriched para-H-3(+) by a factor of similar to 1.25 in comparison to H-3(+) produced from normal H-2 (ortho:para=3:1). The ratio of the rate coefficients of pure para-H-3(+) to that of pure ortho-H-3(+) is inferred to be similar to 2 at low collision energies; the corresponding ratio of the thermal rate coefficients is similar to 1.5 at electron temperatures from 60 to 1000 K. We conclude that this difference is unlikely to have an impact on the interstellar ortho:para ratio of H-3(+).
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