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Wild R, Nötzold M, Simpson M, Tran TD, Wester R. Tunnelling measured in a very slow ion-molecule reaction. Nature 2023; 615:425-429. [PMID: 36859549 DOI: 10.1038/s41586-023-05727-z] [Citation(s) in RCA: 10] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2022] [Accepted: 01/12/2023] [Indexed: 03/03/2023]
Abstract
Quantum tunnelling reactions play an important role in chemistry when classical pathways are energetically forbidden1, be it in gas-phase reactions, surface diffusion or liquid-phase chemistry. In general, such tunnelling reactions are challenging to calculate theoretically, given the high dimensionality of the quantum dynamics, and also very difficult to identify experimentally2-4. Hydrogenic systems, however, allow for accurate first-principles calculations. In this way the rate of the gas-phase proton-transfer tunnelling reaction of hydrogen molecules with deuterium anions, H2 + D- → H- + HD, has been calculated5, but has so far lacked experimental verification. Here we present high-sensitivity measurements of the reaction rate carried out in a cryogenic 22-pole ion trap. We observe an extremely low rate constant of (5.2 ± 1.6) × 10-20 cm3 s-1. This measured value agrees with quantum tunnelling calculations, serving as a benchmark for molecular theory and advancing the understanding of fundamental collision processes. A deviation of the reaction rate from linear scaling, which is observed at high H2 densities, can be traced back to previously unobserved heating dynamics in radiofrequency ion traps.
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Affiliation(s)
- Robert Wild
- Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Innsbruck, Austria
| | - Markus Nötzold
- Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Innsbruck, Austria
| | - Malcolm Simpson
- Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Innsbruck, Austria
| | - Thuy Dung Tran
- Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Innsbruck, Austria
- Department of Optics, Palacký University, Olomouc, Czech Republic
| | - Roland Wester
- Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Innsbruck, Austria.
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2
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Jarrold CC. Probing Anion-Molecule Complexes of Atmospheric Relevance Using Anion Photoelectron Detachment Spectroscopy. ACS PHYSICAL CHEMISTRY AU 2022; 3:17-29. [PMID: 36718261 PMCID: PMC9881448 DOI: 10.1021/acsphyschemau.2c00060] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/30/2022] [Revised: 12/08/2022] [Accepted: 12/09/2022] [Indexed: 01/01/2023]
Abstract
Bimolecular reaction and collision complexes that drive atmospheric chemistry and contribute to the absorption of solar radiation are fleeting and therefore inherently challenging to study experimentally. Furthermore, primary anions in the troposphere are short lived because of a complicated web of reactions and complex formation they undergo, making details of their early fate elusive. In this perspective, the experimental approach of photodetaching mass-selected anion-molecule complexes or complex anions, which prepares neutrals in various vibronic states, is surveyed. Specifically, the application of anion photoelectron spectroscopy along with photoelectron-photofragment coincidence spectroscopy toward the study of collision complexes, complex anions in which a partial covalent bond is formed, and radical bimolecular reaction complexes, with relevance in tropospheric chemistry, will be highlighted.
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3
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Schmid PC, Asvany O, Salomon T, Thorwirth S, Schlemmer S. Leak-Out Spectroscopy, A Universal Method of Action Spectroscopy in Cold Ion Traps. J Phys Chem A 2022; 126:8111-8117. [DOI: 10.1021/acs.jpca.2c05767] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Philipp C. Schmid
- I. Physikalisches Institut der Universität zu Köln, Köln 50937, Germany
| | - Oskar Asvany
- I. Physikalisches Institut der Universität zu Köln, Köln 50937, Germany
| | - Thomas Salomon
- I. Physikalisches Institut der Universität zu Köln, Köln 50937, Germany
| | - Sven Thorwirth
- I. Physikalisches Institut der Universität zu Köln, Köln 50937, Germany
| | - Stephan Schlemmer
- I. Physikalisches Institut der Universität zu Köln, Köln 50937, Germany
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Zhelyazkova V, Martins FBV, Merkt F. Multipole-moment effects in ion-molecule reactions at low temperatures: part III - the He + + CH 4 and He + + CD 4 reactions at low collision energies and the effect of the charge-octupole interaction. Phys Chem Chem Phys 2022; 24:16360-16373. [PMID: 35762649 PMCID: PMC9258730 DOI: 10.1039/d1cp05861d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We present experimental and theoretical studies of the He+ + CH4 and He+ + CD4 reactions at collision energies in the kB·(0-10) K range. Helium atoms in a supersonic beam are excited to a low-field-seeking Rydberg-Stark state and merged with a supersonic beam of CH4 or CD4 using a curved surface-electrode deflector. The ion-molecule reactions are studied within the orbit of the helium Rydberg [He(n)] electron, which suppresses stray-electric-fields-induced heating and makes it possible to reach very low collision energies. The collision energy is varied by adjusting the velocity of the He(n) atoms with the surface deflector, keeping the velocity of the methane beam constant. The reaction product ions (C(H/D)p+ with p∈ {1,2,3}) are collected in a time-of-flight mass spectrometer and monitored as a function of the collision energy. No significant energy-dependence of the total reaction yields of either reactions is observed. The measured relative reaction rate coefficient for the He+ + CH4 reaction is approximately twice higher than the one for the He+ + CD4 reaction. The CH+, CH2+ and CH3+ (CD+, CD2+ and CD3+) ions were detected in ratios 0.28(±0.04) : 1.00(±0.11) : 0.11(±0.04) [0.35(±0.07) : 1.00(±0.16):0.04+0.09-0.04]. We also present calculations of the capture rate coefficients for the two reactions, in which the interaction between the charge of the helium ion and the octupole moment of the methane molecule is included. The rotational-state-specific capture rate coefficients are calculated for states with J = (0-3) at collision energies below kB·15 K. After averaging over the rotational states of methane populated at the rotational temperature of the supersonic beam, the calculations only predict extremely weak enhancements (in the order of ∼0.4%) of the rate coefficients compared to the Langevin rate constant kL over the collision-energy range considered.
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Zhelyazkova V, Martins FBV, Žeško M, Merkt F. Multipole-moment effects in ion-molecule reactions at low temperatures: part II - charge-quadrupole-interaction-induced suppression of the He + + N 2 reaction at collision energies below kB·10 K. Phys Chem Chem Phys 2022; 24:2843-2858. [PMID: 35050290 PMCID: PMC8809083 DOI: 10.1039/d1cp04798a] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2021] [Accepted: 12/23/2021] [Indexed: 11/22/2022]
Abstract
We report on an experimental and theoretical investigation of the He+ + N2 reaction at collision energies in the range between 0 and kB·10 K. The reaction is studied within the orbit of a highly excited Rydberg electron after merging a beam of He Rydberg atoms (He(n), n is the principal quantum number), with a supersonic beam of ground-state N2 molecules using a surface-electrode Rydberg-Stark decelerator and deflector. The collision energy Ecoll is varied by changing the velocity of the He(n) atoms for a fixed velocity of the N2 beam and the relative yields of the ionic reaction products N+ and N2+ are monitored in a time-of-flight mass spectrometer. We observe a reduction of the total reaction-product yield of ∼30% as Ecoll is reduced from ≈kB·10 K to zero. An adiabatic capture model is used to calculate the rotational-state-dependent interaction potentials experienced by the N2 molecules in the electric field of the He+ ion and the corresponding collision-energy-dependent capture rate coefficients. The total collision-energy-dependent capture rate coefficient is then determined by summing over the contributions of the N2 rotational states populated at the 7.0 K rotational temperature of the supersonic beam. The measured and calculated rate coefficients are in good agreement, which enables us to attribute the observed reduction of the reaction rate at low collision energies to the negative quadrupole moment, Qzz, of the N2 molecules. The effect of the sign of the quadrupole moment is illustrated by calculations of the rotational-state-dependent capture rate coefficients for ion-molecule reactions involving N2 (negative Qzz value) and H2 (positive Qzz value) for |J, M〉 rotational states with J ≤ 5 (M is the quantum number associated with the projection of the rotational angular momentum vector J⃑ on the collision axis). With decreasing value of |M|, J⃑ gradually aligns perpendicularly to the collision axis, leading to increasingly repulsive (attractive) interaction potentials for diatomic molecules with positive (negative) Qzz values and to reaction rate coefficients that decrease (increase) with decreasing collision energies.
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Affiliation(s)
| | | | - Matija Žeško
- Laboratory for Physical Chemistry, ETH Zurich, CH-8093 Zurich, Switzerland.
| | - Frédéric Merkt
- Laboratory for Physical Chemistry, ETH Zurich, CH-8093 Zurich, Switzerland.
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Dobulis MA, McGee CJ, Sommerfeld T, Jarrold CC. Autodetachment over Broad Photon Energy Ranges in the Anion Photoelectron Spectra of [O 2- M] - ( M = Glyoxal, Methylglyoxal, or Biacetyl) Complex Anions. J Phys Chem A 2021; 125:9128-9142. [PMID: 34623818 DOI: 10.1021/acs.jpca.1c07163] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Complexes of anion-neutral pairs are prevalent in chemical and physical processes in the interstellar medium, the atmosphere, and biological systems, among others. However, bimolecular anionic species that cannot be described as simple ion-molecule complexes due to their competitive electron affinities have received less attention. In this study, the [O2-M]- (M = glyoxal, methylglyoxal, or biacetyl) anion photoelectron spectra obtained with several different photon energies are reported and interpreted in the context of ab initio calculations. The spectra do not resemble the photoelectron spectra of M- or O2- "solvated" by a neutral partner. Rather, all spectra are dominated by near-threshold autodetachment from what are likely transient dipole bound states of the cis conformers of the complex anions. Very low Franck-Condon overlap between the neutral M·O2 van der Waals clusters and the partial covalently bound complex anions results in low-intensity, broad direct detachment observed in the spectra. The [O2-glyoxal]- spectra measured with 2.88 and 3.495 eV photon energies additionally exhibit features at ∼0.5 eV electron kinetic energy, which is more difficult to explain, though there are numerous quasibound states of the anion that may be involved. Overall, these features point to the inadequacy of describing the complex anions as simple ion-molecule complexes.
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Affiliation(s)
- Marissa A Dobulis
- Department of Chemistry, Indiana University, 800 East Kirkwood Avenue, Bloomington, Indiana 47405, United States
| | - Conor J McGee
- Department of Chemistry, Indiana University, 800 East Kirkwood Avenue, Bloomington, Indiana 47405, United States
| | - Thomas Sommerfeld
- Department of Chemistry and Physics, Southeast Louisiana University, SLU 10878, Hammond, Louisiana 70402, United States
| | - Caroline Chick Jarrold
- Department of Chemistry, Indiana University, 800 East Kirkwood Avenue, Bloomington, Indiana 47405, United States
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Zhelyazkova V, Martins FBV, Agner JA, Schmutz H, Merkt F. Multipole-moment effects in ion-molecule reactions at low temperatures: part I - ion-dipole enhancement of the rate coefficients of the He + + NH 3 and He + + ND 3 reactions at collisional energies Ecoll/ kB near 0 K. Phys Chem Chem Phys 2021; 23:21606-21622. [PMID: 34569565 PMCID: PMC8494273 DOI: 10.1039/d1cp03116c] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2021] [Accepted: 09/02/2021] [Indexed: 11/29/2022]
Abstract
The energy dependence of the rates of the reactions between He+ and ammonia (NY3, Y = {H,D}), forming NY2+, Y and He as well as NY+, Y2 and He, and the corresponding product branching ratios have been measured at low collision energies Ecoll between 0 and kB·40 K using a recently developed merged-beam technique [Allmendinger et al., ChemPhysChem, 2016, 17, 3596]. To avoid heating of the ions by stray electric fields, the reactions are observed within the large orbit of a highly excited Rydberg electron. A beam of He Rydberg atoms was merged with a supersonic beam of ammonia using a curved surface-electrode Rydberg-Stark deflector, which is also used for adjusting the final velocity of the He Rydberg atoms, and thus the collision energy. A collision-energy resolution of about 200 mK was reached at the lowest Ecoll values. The reaction rate coefficients exhibit a sharp increase at collision energies below ∼kB·5 K and pronounced deviations from Langevin-capture behaviour. The experimental results are interpreted in terms of an adiabatic capture model describing the rotational-state-dependent orientation of the ammonia molecules by the electric field of the He+ atom. The model faithfully describes the experimental observations and enables the identification of three classes of |JKMp〉 rotational states of the ammonia molecules showing different low-energy capture behaviour: (A) high-field-seeking states with |KM| ≥ 1 correlating to the lower component of the umbrella-motion tunnelling doublet at low fields. These states undergo a negative linear Stark shift, which leads to strongly enhanced rate coefficients; (B) high-field-seeking states subject to a quadratic Stark shift at low fields and which exhibit only weak rate enhancements; and (C) low-field-seeking states with |KM| ≥ 1. These states exhibit a positive Stark shift at low fields, which completely suppresses the reactions at low collision energies. Marked differences in the low-energy reactivity of NH3 and ND3-the rate enhancements in ND3 are more pronounced than in NH3-are quantitatively explained by the model. They result from the reduced magnitudes of the tunnelling splitting and rotational intervals in ND3 and the different occupations of the rotational levels in the supersonic beam caused by the different nuclear-spin statistical weights. Thermal capture rate constants are derived from the model for the temperature range between 0 and 10 K relevant for astrochemistry. Comparison of the calculated thermal capture rate coefficients with the absolute reaction rates measured above 27 K by Marquette et al. (Chem. Phys. Lett., 1985, 122, 431) suggests that only 40% of the close collisions are reactive.
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Höveler K, Deiglmayr J, Merkt F. Deviation of the rate of the reaction from Langevin behaviour below 1 K, branching ratios for the and product channels, and product-kinetic-energy distributions. Mol Phys 2021. [DOI: 10.1080/00268976.2021.1954708] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Affiliation(s)
| | - Johannes Deiglmayr
- Laboratory of Physical Chemistry, ETH Zurich, Zurich, Switzerland
- Department of Physics, University of Leipzig, Leipzig, Germany
| | - Frédéric Merkt
- Laboratory of Physical Chemistry, ETH Zurich, Zurich, Switzerland
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9
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Höveler K, Deiglmayr J, Agner JA, Schmutz H, Merkt F. The H 2+ + HD reaction at low collision energies: H 3+/H 2D + branching ratio and product-kinetic-energy distributions. Phys Chem Chem Phys 2021; 23:2676-2685. [PMID: 33480928 DOI: 10.1039/d0cp06107g] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The fully state-selected reactions between H2+ molecules in the X+ 2Σg+(v+ = 0, N+ = 0) state and HD molecules in the X 1Σg+(v = 0, J = 0) state forming H3+ + D and H2D+ + H have been studied at collision energies Ecoll between 0 and kB·30 K with a resolution of about 75 mK at the lowest energies. H2 molecules in a supersonic beam were prepared in Rydberg-Stark states with principal quantum number n = 27 and merged with a supersonic beam of ground-state HD molecules using a curved surface-electrode Rydberg-Stark decelerator and deflector. The reaction between H2+ and HD was studied within the orbit of the Rydberg electron to avoid heating of the ions by stray electric fields. The reaction was observed for well-defined and adjustable time intervals, called reaction-observation windows, between two electric-field pulses. The first pulse swept all ions away from the reaction volume and its falling edge defined the beginning of the reaction-observation window. The second pulse extracted the product ions toward a charged-particle detector located at the end of a time-of-flight tube and its rising edge defined the end of the reaction-observation window. Monitoring and analysing the time-of-flight distributions of the H3+ and H2D+ products in dependence of the duration of the reaction-observation window enabled us to obtain information on the kinetic-energy distribution of the product ions and determine branching ratios of the H3+ + D and H2D+ + H reaction channels. The mean product-kinetic-energy release is 0.46(5) eV, representing 27(3)% of the available energy, and the H3+ + D product branching ratio is 0.225(20). The relative reaction rates correspond closely to Langevin capture rates down to the lowest energies probed experimentally (≈kB·50 mK).
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Affiliation(s)
- Katharina Höveler
- Laboratory of Physical Chemistry, ETH Zurich, CH-8093 Zurich, Switzerland.
| | - Johannes Deiglmayr
- Laboratory of Physical Chemistry, ETH Zurich, CH-8093 Zurich, Switzerland.
| | - Josef A Agner
- Laboratory of Physical Chemistry, ETH Zurich, CH-8093 Zurich, Switzerland.
| | - Hansjürg Schmutz
- Laboratory of Physical Chemistry, ETH Zurich, CH-8093 Zurich, Switzerland.
| | - Frédéric Merkt
- Laboratory of Physical Chemistry, ETH Zurich, CH-8093 Zurich, Switzerland.
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Zhelyazkova V, Martins FBV, Agner JA, Schmutz H, Merkt F. Ion-Molecule Reactions below 1 K: Strong Enhancement of the Reaction Rate of the Ion-Dipole Reaction He^{+}+CH_{3}F. PHYSICAL REVIEW LETTERS 2020; 125:263401. [PMID: 33449728 DOI: 10.1103/physrevlett.125.263401] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/08/2020] [Revised: 10/14/2020] [Accepted: 11/04/2020] [Indexed: 06/12/2023]
Abstract
The reaction between He^{+} and CH_{3}F forming predominantly CH_{2}^{+} and CHF^{+} has been studied at collision energies E_{coll} between 0 and k_{B}·10 K in a merged-beam apparatus. To avoid heating of the ions by stray electric fields, the reaction was observed within the orbit of a highly excited Rydberg electron. Supersonic beams of CH_{3}F and He(n) Rydberg atoms with principal quantum number n=30 and 35 were merged and their relative velocity tuned using a Rydberg-Stark decelerator and deflector, allowing an energy resolution of 150 mK. A strong enhancement of the reaction rate was observed below E_{coll}/k_{B}=1 K. The experimental results are interpreted with an adiabatic capture model that accounts for the state-dependent orientation of the polar CH_{3}F molecules by the Stark effect as they approach the He^{+} ion. The enhancement of the reaction rate at low collision energies is primarily attributed to para-CH_{3}F molecules in the J=1, KM=1 high-field-seeking states, which represent about 8% of the population at the 6 K rotational temperature of the supersonic beam.
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Affiliation(s)
| | | | - Josef A Agner
- Laboratory of Physical Chemistry, ETH Zurich, CH-8093 Zurich, Switzerland
| | - Hansjürg Schmutz
- Laboratory of Physical Chemistry, ETH Zurich, CH-8093 Zurich, Switzerland
| | - Frédéric Merkt
- Laboratory of Physical Chemistry, ETH Zurich, CH-8093 Zurich, Switzerland
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Eriksen JJ, Stopkowicz S, Jagau TC, Helgaker T. Foreword: Prof. Gauss Festschrift. Mol Phys 2020. [DOI: 10.1080/00268976.2020.1817247] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Affiliation(s)
| | - Stella Stopkowicz
- Department Chemie, Johannes Gutenberg-Universität Mainz, Mainz, Germany
| | - Thomas-C. Jagau
- Departement Chemie, Katholieke Universiteit Leuven, Leuven, Belgium
| | - Trygve Helgaker
- Hylleraas Centre for Quantum Molecular Sciences, Department of Chemistry, University of Oslo, Oslo, Norway
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Schmidt S, Plamper D, Jekkel J, Weitzel KM. Self-Reactions in the HBr + (DBr +) + HBr System: A State-Selective Investigation of the Role of Rotation. J Phys Chem A 2020; 124:8461-8468. [PMID: 32960596 DOI: 10.1021/acs.jpca.0c07361] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Self-reactions observed in the HBr+ (DBr+) + HBr system have been investigated using a guided ion-beam experiment under single-collision conditions. The reaction channels observed are proton transfer/hydrogen abstraction (PT/HA) in the case of HBr+ and deuteron transfer/hydrogen abstraction (DT/HA) and charge transfer (CT) in the case of DBr+. HBr+/DBr+ ions have been formed with rotational energies selected using the resonance-enhanced multiphoton ionization (REMPI) formation process. Cross sections have been measured as a function of the rotational energy of the ion, Erot, and of the center-of-mass collision energy, Ecm. In the region of low rotational energies, the cross section for both PT/HA and DT/HA decreases with increasing ion rotation. In this region, the cross section for CT increases with increasing ion rotation. For higher rotational energies, the cross section increases with increasing ion rotation for PT/HA and less pronounced for DT/HA. The cross section for CT becomes independent of ion rotation for high rotational energies. Since all reaction channels are exothermic, all cross sections decrease with increasing Ecm.
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Affiliation(s)
- Sebastian Schmidt
- Philipps-Universität Marburg, Fachbereich Chemie, Marburg 35032, Germany
| | - Dominik Plamper
- Philipps-Universität Marburg, Fachbereich Chemie, Marburg 35032, Germany
| | - Jasmin Jekkel
- Philipps-Universität Marburg, Fachbereich Chemie, Marburg 35032, Germany
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