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Krohn OA, Lewandowski HJ. Cold Ion-Molecule Reactions in the Extreme Environment of a Coulomb Crystal. J Phys Chem A 2024. [PMID: 38359783 DOI: 10.1021/acs.jpca.3c07546] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/17/2024]
Abstract
Coulomb crystals provide a unique environment in which to study ion-neutral gas-phase reactions. In these cold, trapped ensembles, we are able to study the kinetics and dynamics of small molecular systems. These measurements have connections to chemistry in the Interstellar Medium (ISM) and planetary atmospheres. This Feature Article will describe recent work in our laboratory that uses Coulomb crystals to study translationally cold, ion-neutral reactions. We provide a description of how the various affordances of our experimental system allow for detailed studies of the reaction mechanisms and the corresponding products. In particular, we will describe quantum-state resolved reactions, isomer-dependent reactions, and reactions with a rarely studied, astrophysically relevant ion, CCl+.
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Affiliation(s)
- O A Krohn
- JILA and the Department of Physics, University of Colorado, Boulder, Colorado 80309, United States
| | - H J Lewandowski
- JILA and the Department of Physics, University of Colorado, Boulder, Colorado 80309, United States
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2
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Krohn OA, Catani KJ, P Sundar S, Greenberg J, da Silva G, Lewandowski HJ. Reactions of Acetonitrile with Trapped, Translationally Cold Acetylene Cations. J Phys Chem A 2023. [PMID: 37289961 DOI: 10.1021/acs.jpca.3c00914] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
The reaction of the acetylene cation (C2H2+) with acetonitrile (CH3CN) is measured in a linear Paul ion trap coupled to a time-of-flight mass spectrometer. C2H2+ and CH3CN are both noted for their astrochemical abundance and predicted relevance for understanding prebiotic chemistry. The observed primary products are c-C3H3+, C3H4+, and C2NH3+. The latter two products react with excess CH3CN to form the secondary product C2NH4+, protonated acetonitrile. The molecular formula of these ionic products can be verified with the aid of isotope substitution via deuteration of the reactants. Primary product reaction pathways and thermodynamics are investigated with quantum chemical calculations and demonstrate exothermic pathways to two isomers of C2NH3+, two isomers of C3H4+, and the cyclopropenyl cation c-C3H3+. This study deepens our understanding of the dynamics and products of a pertinent ion-molecule reaction between two astrochemically abundant molecules in conditions that mimic those of the interstellar medium.
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Affiliation(s)
- O A Krohn
- Department of Physics, University of Colorado, Boulder, Colorado 80309, United States
- JILA, National Institute of Standards and Technology and University of Colorado, Boulder, Colorado 80309, United States
| | - K J Catani
- Department of Physics, University of Colorado, Boulder, Colorado 80309, United States
- JILA, National Institute of Standards and Technology and University of Colorado, Boulder, Colorado 80309, United States
- Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, Colorado 80303, United States
| | - Srivathsan P Sundar
- Department of Chemical Engineering, The University of Melbourne, Parkville 3010, Victoria, Australia
| | - James Greenberg
- Department of Physics, University of Colorado, Boulder, Colorado 80309, United States
- JILA, National Institute of Standards and Technology and University of Colorado, Boulder, Colorado 80309, United States
| | - G da Silva
- Department of Chemical Engineering, The University of Melbourne, Parkville 3010, Victoria, Australia
| | - H J Lewandowski
- Department of Physics, University of Colorado, Boulder, Colorado 80309, United States
- JILA, National Institute of Standards and Technology and University of Colorado, Boulder, Colorado 80309, United States
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3
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Valadbeigi Y, Gal JF. Noble gas cations as Lewis acids: Adduct formation with Lewis bases with high ionization energies. Chem Phys 2023. [DOI: 10.1016/j.chemphys.2023.111918] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/03/2023]
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4
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Zhelyazkova V, Martins FBV, Schilling S, Merkt F. Reaction of an Ion and a Free Radical near 0 K: He + + NO → He + N + + O. J Phys Chem A 2023; 127:1458-1468. [PMID: 36752385 PMCID: PMC9940198 DOI: 10.1021/acs.jpca.2c08221] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/09/2023]
Abstract
The reactions between ions and free radicals are among the fastest chemical reactions. They are predicted to proceed with large rates, even near 0 K, but so far, this prediction has not been verified experimentally. We report on measurements of the rate coefficient of the reaction between the ion He+ and the free radical NO at collision energies in the range between 0 and ∼ kB·10 K. To avoid heating of the ions by stray electric fields, the reaction is observed within the large orbit of a Rydberg electron of principal quantum number n ≥ 30, which shields the ion from external electric fields without affecting the reaction. Low collision energies are reached by merging a supersonic beam of He Rydberg atoms with a supersonic beam of NO molecules and adjusting their relative velocity using a chip-based Rydberg-Stark decelerator and deflector. We observe a strong enhancement of the reaction rate at collision energies below ∼kB·2 K. This enhancement is interpreted on the basis of adiabatic-channel capture-rate calculations as arising from the near-degenerate rotational levels of opposite parity resulting from the Λ-doubling in the X 2Π1/2 ground state of NO. With these new results, we examine the reliability of broadly used approximate analytic expressions for the thermal rate constants of ion-molecule reactions at low temperatures.
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5
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Plamper D, Fujioka K, Schmidt S, Sun R, Weitzel KM. Ion-molecule reactions in the HBr + + HCl (DCl) system: a combined experimental and theoretical study. Phys Chem Chem Phys 2023; 25:2629-2640. [PMID: 36602406 DOI: 10.1039/d2cp03654a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Reactions in the system HBr+ + HCl (DCl) were investigated inside a guided ion-beam apparatus under single-collision conditions. In the HBr+ + HCl system, the proton transfer (PTHCl) and charge transfer (CT) are observable. In the HBr+ + DCl system, proton transfer (PTDCl) and deuterium abstraction (DA) are accessible. The cross sections for all reaction channels were measured as a function of the collision energy Ecm and of the rotational energy Erot of the ion. The rotationally state-selective formation of the ionic species was realized by resonance-enhanced multiphoton ionization (REMPI). As expected, the PT-channels are exothermic, and the cross section decreases with increasing collision energy for both PTHCl and PTDCl. The cross section for DA also decreases with an increasing Ec.m.. In the case of a considerably endothermic CT-channel, the reaction efficiency increases with increasing collision energy but has an overall much smaller cross sections compared to PT and DA reactions. Both PT-reactions are hindered by ion rotation, whereas DA is independent of Erot. The CT-channel shows a rotational enhancement near the thermochemical threshold. The experiment is complemented by theory, using ab initio molecular dynamics (AIMD, also known as direct dynamics) simulations and taking the rotational enhancement of HBr+ into account. The simulations show good agreement with the experimental results. The cross section of PTHCl decreases with an increase of the rotational energy. Furthermore, the absolute cross sections are in the same order of magnitude. The CT channel shows no reactions in the simulation.
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Affiliation(s)
- Dominik Plamper
- Philipps-Universität Marburg, Fachbereich Chemie, 35032 Marburg, Germany.
| | - Kazuumi Fujioka
- Department of Chemistry, University of Hawai'i at Manoa, Honolulu, Hawaii 96822, USA.
| | - Sebastian Schmidt
- Philipps-Universität Marburg, Fachbereich Chemie, 35032 Marburg, Germany.
| | - Rui Sun
- Department of Chemistry, University of Hawai'i at Manoa, Honolulu, Hawaii 96822, USA.
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6
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Okada K, Sakimoto K, Schuessler HA. Rotational Cooling Effect on the Rate Constant in the CH 3F + Ca + Reaction at Low Collision Energies. J Phys Chem A 2022; 126:4881-4890. [PMID: 35857026 DOI: 10.1021/acs.jpca.2c01063] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The rotational cooling effect on the reaction rate constant of the gas-phase ion-polar-molecule reaction CH3F + Ca+ → CH3 + CaF+ was experimentally studied at low collision energies. Fluoromethane molecules showed higher reactivity as the rotational temperature decreased. The experimental rate constants were compared with the capture rate constants which were obtained by the Perturbed Rotational State (PRS) theory assuming the rotational level distribution corresponding to the experimental conditions. The PRS result shows a strong dependence of the capture rate constants on the rotational level distribution in accordance with the experimental findings. However, the PRS capture rate constants deviate from the measurement values as the average collision energy increases especially when the fluoromethane molecules are rotationally cooled far below room temperature. The present paper suggests that the rotational state distribution significantly affects the rate constants of ion-polar-molecule reactions and is one of the important issues to be considered in the study of molecular synthesis in the interstellar medium, where the thermal equilibrium is not necessarily established.
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Affiliation(s)
- Kunihiro Okada
- Department of Materials and Life Sciences, Sophia University, 7-1 Kioicho, Chiyoda, Tokyo 102-8554, Japan
| | - Kazuhiro Sakimoto
- Department of Materials and Life Sciences, Sophia University, 7-1 Kioicho, Chiyoda, Tokyo 102-8554, Japan
| | - Hans A Schuessler
- Department of Physics and Astronomy, Texas A&M University, College Station, Texas 77843-4242, United States
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7
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Tsikritea A, Diprose JA, Softley TP, Heazlewood BR. Capture Theory Models: An overview of their development, experimental verification, and applications to ion-molecule reactions. J Chem Phys 2022; 157:060901. [DOI: 10.1063/5.0098552] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Since Arrhenius first proposed an equation to account for the behaviour of thermally activated reactions in 1889, significant progress has been made in our understanding of chemical reactivity. A number of capture theory models have been developed over the past several decades to predict the rate coefficients for reactions between ions and molecules-ranging from the Langevin equation (for reactions between ions and non-polar molecules) to more recent fully quantum theories (for reactions at ultra-cold temperatures). A number of different capture theory methods are discussed, with the key assumptions underpinning each approach clearly set out. The strengths and limitations of these capture theory methods are examined through detailed comparisons between low-temperature experimental measurements and capture theory predictions. Guidance is provided on the selection of an appropriate capture theory method for a given class of ion-molecule reaction and set of experimental conditions-identifying when a capture-based model is likely to provide an accurate prediction. Finally, the impact of capture theories on fields such as astrochemical modelling is noted, with some potential future directions of capture-based approaches outlined.
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Affiliation(s)
| | - Jake A Diprose
- University of Liverpool Department of Physics, United Kingdom
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8
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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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9
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Greenberg J, Krohn OA, Bossert JA, Shyur Y, Macaluso D, Fitch NJ, Lewandowski HJ. Velocity-tunable beam of continuously decelerated polar molecules for cold ion-molecule reaction studies. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2021; 92:103202. [PMID: 34717395 DOI: 10.1063/5.0057859] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/25/2021] [Accepted: 09/24/2021] [Indexed: 06/13/2023]
Abstract
Producing high densities of molecules is a fundamental challenge for low-temperature, ion-molecule reaction studies. Traveling-wave Stark decelerators promise to deliver high density beams of cold, polar molecules but require non-trivial control of high-voltage potentials. We have overcome this experimental challenge and demonstrate continuous deceleration of ND3 from 385 to 10 m/s, while driving the decelerator electrodes with a 10 kV amplitude sinewave. In addition, we test an alternative slowing scheme, which increases the time delay between decelerated packets of ND3 and non-decelerated molecules, allowing for better energy resolution of subsequent reaction studies. We characterize this source of neutral, polar molecules suitable for energy-resolved reaction studies with trapped ions at cold translational temperatures. We also propose a combined apparatus consisting of the traveling-wave decelerator and a linear ion trap with a time-of-flight mass spectrometer and discuss to what extent it may achieve cold, energy-resolved, ion-neutral reactions.
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Affiliation(s)
- James Greenberg
- Department of Physics, University of Colorado, Boulder, Colorado 80309, USA
| | - O A Krohn
- Department of Physics, University of Colorado, Boulder, Colorado 80309, USA
| | - Jason A Bossert
- Department of Physics, University of Colorado, Boulder, Colorado 80309, USA
| | - Yomay Shyur
- Department of Physics, University of Colorado, Boulder, Colorado 80309, USA
| | - David Macaluso
- Department of Physics, University of Colorado, Boulder, Colorado 80309, USA
| | - N J Fitch
- Department of Physics, University of Colorado, Boulder, Colorado 80309, USA
| | - H J Lewandowski
- Department of Physics, University of Colorado, Boulder, Colorado 80309, USA
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10
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Tsikritea A, Park K, Bertier P, Loreau J, Softley TP, Heazlewood BR. Inverse kinetic isotope effects in the charge transfer reactions of ammonia with rare gas ions. Chem Sci 2021; 12:10005-10013. [PMID: 34377395 PMCID: PMC8317658 DOI: 10.1039/d1sc01652k] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2021] [Accepted: 06/21/2021] [Indexed: 11/21/2022] Open
Abstract
In the absence of experimental data, models of complex chemical environments rely on predicted reaction properties. Astrochemistry models, for example, typically adopt variants of capture theory to estimate the reactivity of ionic species present in interstellar environments. In this work, we examine astrochemically-relevant charge transfer reactions between two isotopologues of ammonia, NH3 and ND3, and two rare gas ions, Kr+ and Ar+. An inverse kinetic isotope effect is observed; ND3 reacts faster than NH3. Combining these results with findings from an earlier study on Xe+ (Petralia et al., Nat. Commun., 2020, 11, 1), we note that the magnitude of the kinetic isotope effect shows a dependence on the identity of the rare gas ion. Capture theory models consistently overestimate the reaction rate coefficients and cannot account for the observed inverse kinetic isotope effects. In all three cases, the reactant and product potential energy surfaces, constructed from high-level ab initio calculations, do not exhibit any energetically-accessible crossing points. Aided by a one-dimensional quantum-mechanical model, we propose a possible explanation for the presence of inverse kinetic isotope effects in these charge transfer reaction systems.
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Affiliation(s)
- A Tsikritea
- Department of Chemistry, University of Oxford, Physical and Theoretical Chemistry South Parks Road Oxford OX1 3QZ UK
- Department of Physics, University of Liverpool Liverpool L69 7ZE UK
| | - K Park
- Department of Chemistry, University of Oxford, Physical and Theoretical Chemistry South Parks Road Oxford OX1 3QZ UK
| | - P Bertier
- Department of Chemistry, University of Oxford, Physical and Theoretical Chemistry South Parks Road Oxford OX1 3QZ UK
| | - J Loreau
- KU Leuven, Department of Chemistry Celestijnenlaan 200F B-3001 Leuven Belgium
| | - T P Softley
- School of Chemistry, University of Birmingham Edgbaston B15 2TT UK
| | - B R Heazlewood
- Department of Physics, University of Liverpool Liverpool L69 7ZE UK
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11
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Abstract
The prospect of cooling matter down to temperatures that are close to absolute zero raises intriguing questions about how chemical reactivity changes under these extreme conditions. Although some types of chemical reaction still occur at 1 μK, they can no longer adhere to the conventional picture of reactants passing over an activation energy barrier to become products. Indeed, at ultracold temperatures, the system enters a fully quantum regime, and quantum mechanics replaces the classical picture of colliding particles. In this Review, we discuss recent experimental and theoretical developments that allow us to explore chemical reactions at temperatures that range from 100 K to 500 nK. Although the field is still in its infancy, exceptional control has already been demonstrated over reactivity at low temperatures.
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12
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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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13
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Okada K, Sakimoto K, Takada Y, Schuessler HA. A study of the translational temperature dependence of the reaction rate constant between CH 3CN and Ne + at low temperatures. J Chem Phys 2020; 153:124305. [PMID: 33003759 DOI: 10.1063/5.0013807] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
We have measured the translational temperature dependence of the reaction rate constant for CH3CN + Ne+ → products at low temperatures. A cold Ne+ ensemble was embedded in Ca+ Coulomb crystals by a sympathetic laser cooling technique, while cold acetonitrile (CH3CN) molecules were produced by two types of Stark velocity filters to widely change the translational temperatures. The measured reaction rate constant gradually increases with the decrease in the translational temperature of the velocity-selected CH3CN molecules from 60 K down to 2 K, and thereby, a steep increase was observed at temperatures lower than 5 K. A comparison between experimental rate constants and the ion-dipole capture rate constants by the Perturbed Rotational State (PRS) theory was performed. The PRS capture rate constant reproduces well the reaction rate constant at a few kelvin but not for temperatures higher than 5 K. The result indicates that the reaction probability is small compared to typical ion-polar molecule reactions at temperatures above 5 K.
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Affiliation(s)
- Kunihiro Okada
- Department of Physics, Sophia University, 7-1 Kioicho, Chiyoda, Tokyo 102-8554, Japan
| | - Kazuhiro Sakimoto
- Department of Physics, Sophia University, 7-1 Kioicho, Chiyoda, Tokyo 102-8554, Japan
| | - Yusuke Takada
- Department of Physics, Sophia University, 7-1 Kioicho, Chiyoda, Tokyo 102-8554, Japan
| | - Hans A Schuessler
- Department of Physics and Astronomy, Texas A&M University, College Station, Texas 77843-4242, USA
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14
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Strong inverse kinetic isotope effect observed in ammonia charge exchange reactions. Nat Commun 2020; 11:173. [PMID: 31924778 PMCID: PMC6954264 DOI: 10.1038/s41467-019-13976-8] [Citation(s) in RCA: 24] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2019] [Accepted: 12/12/2019] [Indexed: 11/09/2022] Open
Abstract
Isotopic substitution has long been used to understand the detailed mechanisms of chemical reactions; normally the substitution of hydrogen by deuterium leads to a slower reaction. Here, we report our findings on the charge transfer collisions of cold [Formula: see text] ions and two isotopologues of ammonia, [Formula: see text] and [Formula: see text]. Deuterated ammonia is found to react more than three times faster than hydrogenated ammonia. Classical capture models are unable to account for this pronounced inverse kinetic isotope effect. Moreover, detailed ab initio calculations cannot identify any (energetically accessible) crossing points between the reactant and product potential energy surfaces, indicating that electron transfer is likely to be slow. The higher reactivity of [Formula: see text] is attributed to the greater density of states (and therefore lifetime) of the deuterated reaction complex compared to the hydrogenated system. Our observations could provide valuable insight into possible mechanisms contributing to deuterium fractionation in the interstellar medium.
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15
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Schmid PC, Miller MI, Greenberg J, Nguyen TL, Stanton JF, Lewandowski HJ. Quantum-state-specific reaction rate measurements for the photo-induced reaction Ca+ + O2 → CaO+ + O. Mol Phys 2019. [DOI: 10.1080/00268976.2019.1622811] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Affiliation(s)
- Philipp C. Schmid
- JILA and the Department of Physics, University of Colorado, Boulder, Colorado, USA
| | - Mikhail I. Miller
- JILA and the Department of Physics, University of Colorado, Boulder, Colorado, USA
| | - James Greenberg
- JILA and the Department of Physics, University of Colorado, Boulder, Colorado, USA
| | - Thanh L. Nguyen
- Quantum Theory Project, Departments of Chemistry and Physics, University of Florida, Gainesville, Florida, USA
| | - John F. Stanton
- Quantum Theory Project, Departments of Chemistry and Physics, University of Florida, Gainesville, Florida, USA
| | - H. J. Lewandowski
- JILA and the Department of Physics, University of Colorado, Boulder, Colorado, USA
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16
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Rivlin T, McKemmish LK, Spinlove KE, Tennyson J. Low temperature scattering with the R-matrix method: argon-argon scattering. Mol Phys 2019. [DOI: 10.1080/00268976.2019.1615143] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Affiliation(s)
- Tom Rivlin
- Department of Physics and Astronomy, University College London, London, UK
| | - Laura K. McKemmish
- Department of Physics and Astronomy, University College London, London, UK
- Department of Chemistry, University of New South Wales, Sydney, Australia
| | - K. Eryn Spinlove
- Department of Physics and Astronomy, University College London, London, UK
| | - Jonathan Tennyson
- Department of Physics and Astronomy, University College London, London, UK
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17
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Affiliation(s)
- Brianna R. Heazlewood
- Department of Chemistry, Physical and Theoretical Chemistry Laboratory, University of Oxford, Oxford, United Kingdom
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18
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Brand C, Stickler BA, Knobloch C, Shayeghi A, Hornberger K, Arndt M. Conformer Selection by Matter-Wave Interference. PHYSICAL REVIEW LETTERS 2018; 121:173002. [PMID: 30411911 DOI: 10.1103/physrevlett.121.173002] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/02/2017] [Indexed: 06/08/2023]
Abstract
We establish that matter-wave diffraction at near-resonant ultraviolet optical gratings can be used to spatially separate individual conformers of complex molecules. Our calculations show that the conformational purity of the prepared beam can be close to 100% and that all molecules remain in their electronic ground state. The proposed technique is independent of the dipole moment and the spin of the molecule and thus paves the way for structure-sensitive experiments with hydrocarbons and biomolecules, such as neurotransmitters and hormones, which have evaded conformer-pure isolation so far.
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Affiliation(s)
- Christian Brand
- University of Vienna, Faculty of Physics, Boltzmanngasse 5, A-1090 Vienna, Austria
| | - Benjamin A Stickler
- Faculty of Physics, University of Duisburg-Essen, Lotharstraße 1, 47048 Duisburg, Germany
| | - Christian Knobloch
- University of Vienna, Faculty of Physics, Boltzmanngasse 5, A-1090 Vienna, Austria
| | - Armin Shayeghi
- University of Vienna, Faculty of Physics, Boltzmanngasse 5, A-1090 Vienna, Austria
| | - Klaus Hornberger
- Faculty of Physics, University of Duisburg-Essen, Lotharstraße 1, 47048 Duisburg, Germany
| | - Markus Arndt
- University of Vienna, Faculty of Physics, Boltzmanngasse 5, A-1090 Vienna, Austria
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19
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Schmid PC, Greenberg J, Miller MI, Loeffler K, Lewandowski HJ. An ion trap time-of-flight mass spectrometer with high mass resolution for cold trapped ion experiments. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2017; 88:123107. [PMID: 29289207 DOI: 10.1063/1.4996911] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Trapping molecular ions that have been sympathetically cooled with laser-cooled atomic ions is a useful platform for exploring cold ion chemistry. We designed and characterized a new experimental apparatus for probing chemical reaction dynamics between molecular cations and neutral radicals at temperatures below 1 K. The ions are trapped in a linear quadrupole radio-frequency trap and sympathetically cooled by co-trapped, laser-cooled, atomic ions. The ion trap is coupled to a time-of-flight mass spectrometer to readily identify product ion species and to accurately determine trapped ion numbers. We discuss, and present in detail, the design of this ion trap time-of-flight mass spectrometer and the electronics required for driving the trap and mass spectrometer. Furthermore, we measure the performance of this system, which yields mass resolutions of m/Δm ≥ 1100 over a wide mass range, and discuss its relevance for future measurements in chemical reaction kinetics and dynamics.
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Affiliation(s)
- P C Schmid
- JILA and the Department of Physics, University of Colorado, Boulder, Colorado 80309-0440, USA
| | - J Greenberg
- JILA and the Department of Physics, University of Colorado, Boulder, Colorado 80309-0440, USA
| | - M I Miller
- JILA and the Department of Physics, University of Colorado, Boulder, Colorado 80309-0440, USA
| | - K Loeffler
- JILA and the Department of Physics, University of Colorado, Boulder, Colorado 80309-0440, USA
| | - H J Lewandowski
- JILA and the Department of Physics, University of Colorado, Boulder, Colorado 80309-0440, USA
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20
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Affiliation(s)
- Stefan Willitsch
- Department of Chemistry; University of Basel; Klingelbergstrasse 80, 4056 Basel Switzerland
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21
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Okada K, Takada Y, Kimura N, Wada M, Schuessler HA. Development of a wavy Stark velocity filter for studying interstellar chemistry. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2017; 88:083106. [PMID: 28863702 DOI: 10.1063/1.4997721] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Cold polar molecules are key to both the understanding of fundamental physics and the characterization of the chemical evolution of interstellar clouds. To facilitate such studies over a wide range of temperatures, we developed a new type of Stark velocity filter for changing the translational and rotational temperatures of velocity-selected polar molecules without changing the output beam position. The translational temperature of guided polar molecules can be significantly varied by exchanging the wavy deflection section with one having a different radius of the curvature and a different deflection angle. Combining in addition a temperature variable gas cell with the wavy Stark velocity filter enables to observe the translational and rotational temperature dependence of the reaction-rate constants of cold ion-polar molecule reactions over the interesting temperature range of 10-100 K.
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Affiliation(s)
- Kunihiro Okada
- Department of Physics, Sophia University, 7-1 Kioicho, Chiyoda, Tokyo 102-8554, Japan
| | - Yusuke Takada
- Department of Physics, Sophia University, 7-1 Kioicho, Chiyoda, Tokyo 102-8554, Japan
| | - Naoki Kimura
- Department of Physics, Sophia University, 7-1 Kioicho, Chiyoda, Tokyo 102-8554, Japan
| | - Michiharu Wada
- RIKEN Nishina Center for Accelerator-Based Science, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
| | - Hans A Schuessler
- Department of Physics and Astronomy, Texas A&M University, College Station, Texas 77843, USA
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22
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Allmendinger P, Deiglmayr J, Schullian O, Höveler K, Agner JA, Schmutz H, Merkt F. New Method to Study Ion–Molecule Reactions at Low Temperatures and Application to the Reaction. Chemphyschem 2016; 17:3596-3608. [DOI: 10.1002/cphc.201600828] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2016] [Indexed: 11/06/2022]
Affiliation(s)
- Pitt Allmendinger
- Laboratorium für Physikalische Chemie, Vladimir-Prelog-Weg 2 ETH Zürich CH-8093 Zurich Switzerland
| | - Johannes Deiglmayr
- Laboratorium für Physikalische Chemie, Vladimir-Prelog-Weg 2 ETH Zürich CH-8093 Zurich Switzerland
| | - Otto Schullian
- Laboratorium für Physikalische Chemie, Vladimir-Prelog-Weg 2 ETH Zürich CH-8093 Zurich Switzerland
| | - Katharina Höveler
- Laboratorium für Physikalische Chemie, Vladimir-Prelog-Weg 2 ETH Zürich CH-8093 Zurich Switzerland
| | - Josef A. Agner
- Laboratorium für Physikalische Chemie, Vladimir-Prelog-Weg 2 ETH Zürich CH-8093 Zurich Switzerland
| | - Hansjürg Schmutz
- Laboratorium für Physikalische Chemie, Vladimir-Prelog-Weg 2 ETH Zürich CH-8093 Zurich Switzerland
| | - Frédéric Merkt
- Laboratorium für Physikalische Chemie, Vladimir-Prelog-Weg 2 ETH Zürich CH-8093 Zurich Switzerland
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23
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Eberle P, Dörfler AD, von Planta C, Ravi K, Willitsch S. A Dynamic Ion–Atom Hybrid Trap for High‐Resolution Cold‐Collision Studies. Chemphyschem 2016; 17:3769-3775. [DOI: 10.1002/cphc.201600643] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2016] [Indexed: 11/10/2022]
Affiliation(s)
- Pascal Eberle
- Department of Chemistry University of Basel Klingelbergstrasse 80 4056 Basel Switzerland
| | - Alexander D. Dörfler
- Department of Chemistry University of Basel Klingelbergstrasse 80 4056 Basel Switzerland
| | - Claudio von Planta
- Department of Chemistry University of Basel Klingelbergstrasse 80 4056 Basel Switzerland
| | - Krishnamurthy Ravi
- Department of Chemistry University of Basel Klingelbergstrasse 80 4056 Basel Switzerland
| | - Stefan Willitsch
- Department of Chemistry University of Basel Klingelbergstrasse 80 4056 Basel Switzerland
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24
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Abstract
Coulomb crystals-as a source of translationally cold, highly localized ions-are being increasingly utilized in the investigation of ion-molecule reaction dynamics in the cold regime. To develop a fundamental understanding of ion-molecule reactions, and to challenge existing models that describe the rates, product branching ratios, and temperature dependence of such processes, investigators need to exercise full control over the experimental reaction parameters. This requires not only state selection of the reactants, but also control over the collision process (e.g., the collisional energy and angular momentum) and state-selective product detection. The combination of Coulomb crystals in ion traps with cold neutral-molecule sources is enabling the measurement of state-selective reaction rates in a diverse range of systems. With the development of appropriate product detection techniques, we are moving toward the ultimate goal of examining low-energy, state-to-state ion-molecule reaction dynamics.
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25
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Deb N, Heazlewood BR, Rennick CJ, Softley TP. Laser induced rovibrational cooling of the linear polyatomic ion C2H2+. J Chem Phys 2014; 140:164314. [DOI: 10.1063/1.4870644] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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26
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Rösch D, Willitsch S, Chang YP, Küpper J. Chemical reactions of conformationally selected 3-aminophenol molecules in a beam with Coulomb-crystallized Ca+ ions. J Chem Phys 2014; 140:124202. [PMID: 24697433 DOI: 10.1063/1.4869100] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Daniel Rösch
- Department of Chemistry, University of Basel, Klingelbergstrasse 80, 4056 Basel, Switzerland
| | - Stefan Willitsch
- Department of Chemistry, University of Basel, Klingelbergstrasse 80, 4056 Basel, Switzerland
| | - Yuan-Pin Chang
- Center for Free-Electron Laser Science, DESY, Notkestrasse 85, 22607 Hamburg, Germany
| | - Jochen Küpper
- Center for Free-Electron Laser Science, DESY, Notkestrasse 85, 22607 Hamburg, Germany
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27
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Dulitz K, Motsch M, Vanhaecke N, Softley TP. Getting a grip on the transverse motion in a Zeeman decelerator. J Chem Phys 2014; 140:104201. [PMID: 24628161 DOI: 10.1063/1.4866906] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
Zeeman deceleration is an experimental technique in which inhomogeneous, time-dependent magnetic fields generated inside an array of solenoid coils are used to manipulate the velocity of a supersonic beam. A 12-stage Zeeman decelerator has been built and characterized using hydrogen atoms as a test system. The instrument has several original features including the possibility to replace each deceleration coil individually. In this article, we give a detailed description of the experimental setup, and illustrate its performance. We demonstrate that the overall acceptance in a Zeeman decelerator can be significantly increased with only minor changes to the setup itself. This is achieved by applying a rather low, anti-parallel magnetic field in one of the solenoid coils that forms a temporally varying quadrupole field, and improves particle confinement in the transverse direction. The results are reproduced by three-dimensional numerical particle trajectory simulations thus allowing for a rigorous analysis of the experimental data. The findings suggest the use of a modified coil configuration to improve transverse focusing during the deceleration process.
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Affiliation(s)
- Katrin Dulitz
- Department of Chemistry, Chemistry Research Laboratory, University of Oxford, 12 Mansfield Road, Oxford OX1 3TA, United Kingdom
| | - Michael Motsch
- Laboratorium für Physikalische Chemie, ETH Zürich, 8093 Zürich, Switzerland
| | - Nicolas Vanhaecke
- Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany and Laboratoire Aimé Cotton, CNRS, Université Paris-Sud, ENS Cachan, 91405 Orsay, France
| | - Timothy P Softley
- Department of Chemistry, Chemistry Research Laboratory, University of Oxford, 12 Mansfield Road, Oxford OX1 3TA, United Kingdom
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28
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Abstract
Over the past decade, and particularly the past five years, a quiet revolution has been building at the border between atomic physics and experimental quantum chemistry. The rapid development of techniques for producing cold and even ultracold molecules without a perturbing rare-gas cluster shell is now enabling the study of chemical reactions and scattering at the quantum scattering limit with only a few partial waves contributing to the incident channel. Moreover, the ability to perform these experiments with nonthermal distributions comprising one or a few specific states enables the observation and even full control of state-to-state collision rates in this computation-friendly regime: This is perhaps the most elementary study possible of scattering and reaction dynamics.
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Affiliation(s)
- Benjamin K Stuhl
- Joint Quantum Institute, National Institute of Standards and Technology and University of Maryland, Gaithersburg, Maryland 20899
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29
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Brouard M, Parker DH, van de Meerakker SYT. Taming molecular collisions using electric and magnetic fields. Chem Soc Rev 2014; 43:7279-94. [DOI: 10.1039/c4cs00150h] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
In molecular collision experiments, studying the collision process in high detail requires controlling molecular degrees of freedom before the collision.
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Affiliation(s)
- Mark Brouard
- The Department of Chemistry
- University of Oxford
- The Physical and Theoretical Chemistry Laboratory
- Oxford OX1 3QZ, UK
| | - David H. Parker
- Radboud University Nijmegen
- Institute for Molecules and Materials
- 6525 AJ Nijmegen, The Netherlands
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30
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Affiliation(s)
- Mikhail Lemeshko
- a ITAMP, Harvard-Smithsonian Center for Astrophysics , Cambridge , MA , 02138 , USA
- b Physics Department , Harvard University , Cambridge , MA , 02138 , USA
- c Kavli Institute for Theoretical Physics , University of California , Santa Barbara , CA , 93106 , USA
| | - Roman V. Krems
- c Kavli Institute for Theoretical Physics , University of California , Santa Barbara , CA , 93106 , USA
- d Department of Chemistry , University of British Columbia , BC V6T 1Z1, Vancouver , Canada
| | - John M. Doyle
- b Physics Department , Harvard University , Cambridge , MA , 02138 , USA
| | - Sabre Kais
- e Departments of Chemistry and Physics , Purdue University , West Lafayette , IN , 47907 , USA
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31
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Hall FH, Aymar M, Raoult M, Dulieu O, Willitsch S. Light-assisted cold chemical reactions of barium ions with rubidium atoms. Mol Phys 2013. [DOI: 10.1080/00268976.2013.770930] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Affiliation(s)
- Felix H.J. Hall
- a Department of Chemistry , University of Basel , Basel , Switzerland
| | - Mireille Aymar
- b Laboratoire Aimé Cotton , CNRS/Univ Paris-Sud/ENS Cachan , Bât. 505, Campus d’Orsay, 91405, Orsay Cedex , France
| | - Maurice Raoult
- b Laboratoire Aimé Cotton , CNRS/Univ Paris-Sud/ENS Cachan , Bât. 505, Campus d’Orsay, 91405, Orsay Cedex , France
| | - Olivier Dulieu
- b Laboratoire Aimé Cotton , CNRS/Univ Paris-Sud/ENS Cachan , Bât. 505, Campus d’Orsay, 91405, Orsay Cedex , France
| | - Stefan Willitsch
- a Department of Chemistry , University of Basel , Basel , Switzerland
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32
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Hall FH, Eberle P, Hegi G, Raoult M, Aymar M, Dulieu O, Willitsch S. Ion-neutral chemistry at ultralow energies: dynamics of reactive collisions between laser-cooled Ca+ ions and Rb atoms in an ion-atom hybrid trap. Mol Phys 2013. [DOI: 10.1080/00268976.2013.780107] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Affiliation(s)
- Felix H.J. Hall
- Department of Chemistry, University of Basel , Basel, Switzerland
| | - Pascal Eberle
- Department of Chemistry, University of Basel , Basel, Switzerland
| | - Gregor Hegi
- Department of Chemistry, University of Basel , Basel, Switzerland
| | - Maurice Raoult
- Laboratoire Aimé Cotton, CNRS/Univ. Paris-Sud/ENS Cachan , Orsay Cedex, France
| | - Mireille Aymar
- Laboratoire Aimé Cotton, CNRS/Univ. Paris-Sud/ENS Cachan , Orsay Cedex, France
| | - Olivier Dulieu
- Laboratoire Aimé Cotton, CNRS/Univ. Paris-Sud/ENS Cachan , Orsay Cedex, France
| | - Stefan Willitsch
- Department of Chemistry, University of Basel , Basel, Switzerland
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33
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Deb N, Heazlewood BR, Bell MT, Softley TP. Blackbody-mediated rotational laser cooling schemes in MgH+, DCl+, HCl+, LiH and CsH. Phys Chem Chem Phys 2013; 15:14270-81. [DOI: 10.1039/c3cp51839f] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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34
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Hall FHJ, Willitsch S. Millikelvin reactive collisions between sympathetically cooled molecular ions and laser-cooled atoms in an ion-atom hybrid trap. PHYSICAL REVIEW LETTERS 2012; 109:233202. [PMID: 23368197 DOI: 10.1103/physrevlett.109.233202] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/29/2012] [Indexed: 06/01/2023]
Abstract
We report on a study of cold reactive collisions between sympathetically cooled molecular ions and laser-cooled atoms in an ion-atom hybrid trap. Chemical reactions were studied at average collision energies <E(coll)>/k(B)>/~20 mK, about 2 orders of magnitude lower than has been achieved in previous experiments with molecular ions. Choosing N(2)(+)+Rb as a prototypical system, we find that the reaction rate is independent of the collision energy within the range studied, but strongly dependent on the internal state of Rb. Highly efficient charge exchange four times faster than the Langevin rate was observed with Rb in the excited (5p) (2)P(3/2) state. This observation is rationalized by a capture process dominated by the charge-quadrupole interaction and a near resonance between the entrance and exit channels of the system. Our results provide a test of classical models for reactions of molecular ions at the lowest energies reached thus far.
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Affiliation(s)
- Felix H J Hall
- Department of Chemistry, University of Basel, Klingelbergstrasse 80, 4056 Basel, Switzerland
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35
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Willitsch S. Coulomb-crystallised molecular ions in traps: methods, applications, prospects. INT REV PHYS CHEM 2012. [DOI: 10.1080/0144235x.2012.667221] [Citation(s) in RCA: 66] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
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36
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van de Meerakker SYT, Bethlem HL, Vanhaecke N, Meijer G. Manipulation and Control of Molecular Beams. Chem Rev 2012; 112:4828-78. [DOI: 10.1021/cr200349r] [Citation(s) in RCA: 247] [Impact Index Per Article: 20.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
| | - Hendrick L. Bethlem
- Institute for Lasers, Life and
Biophotonics, VU University Amsterdam,
De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands
| | - Nicolas Vanhaecke
- Laboratoire Aimé Cotton, CNRS, Bâtiment 505, Université Paris-Sud,
91405 Orsay, France
| | - Gerard Meijer
- Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin,
Germany
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37
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Hall FHJ, Aymar M, Bouloufa-Maafa N, Dulieu O, Willitsch S. Light-assisted ion-neutral reactive processes in the cold regime: radiative molecule formation versus charge exchange. PHYSICAL REVIEW LETTERS 2011; 107:243202. [PMID: 22242998 DOI: 10.1103/physrevlett.107.243202] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/18/2011] [Indexed: 05/31/2023]
Abstract
We present a combined experimental and theoretical study of cold reactive collisions between laser-cooled Ca+ ions and Rb atoms in an ion-atom hybrid trap. We observe rich chemical dynamics which are interpreted in terms of nonadiabatic and radiative charge exchange as well as radiative molecule formation using high-level electronic structure calculations. We study the role of light-assisted processes and show that the efficiency of the dominant chemical pathways is considerably enhanced in excited reaction channels. Our results illustrate the importance of radiative and nonradiative processes for the cold chemistry occurring in ion-atom hybrid traps.
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Affiliation(s)
- Felix H J Hall
- Department of Chemistry, University of Basel, Klingelbergstrasse 80, 4056 Basel, Switzerland
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38
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Tacconi M, Bovino S, Gianturco FA. Direct and inverse reactions of LiH+ with He(1S) from quantum calculations: mechanisms and rates. Phys Chem Chem Phys 2011; 14:637-45. [PMID: 22086258 DOI: 10.1039/c1cp22315a] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
The gas-phase reaction of LiH(+) (X(2)Σ) with He((1)S) atoms, yielding Li(+)He with a small endothermicity for the rotovibrational ground state of the reagents, is analysed using the quantum reactive approach that employs the Negative Imaginary Potential (NIP) scheme discussed earlier in the literature. The dependence of low-T rates on the initial vibrational state of LiH(+) is analysed and the role of low-energy Feshbach resonances is also discussed. The inverse destruction reaction of LiHe(+), a markedly exothermic process, is also investigated and the rates are computed in the same range of temperatures. The possible roles of these reactions in early universe astrophysical networks, in He droplets environments or in cold traps are briefly discussed.
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Affiliation(s)
- M Tacconi
- Department of Chemistry, Sapienza University of Rome, Rome, Italy
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39
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Georgescu IM, Willitsch S. Theoretical characterization of laser- and sympathetically-cooled ions in surface-electrode ion traps. Phys Chem Chem Phys 2011; 13:18852-8. [PMID: 21643582 DOI: 10.1039/c1cp20733d] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Using molecular dynamics simulations we characterize theoretically Coulomb clusters of laser- and sympathetically-cooled ions in a five-wire surface-electrode ion trap. We show that the asymmetry of the trapping potential leads to significantly different cluster structures and ion energy distributions in comparison to conventionally used linear Paul traps and to an asymmetric segregation of the ions in bi-component Coulomb clusters. We explore the impact of our results on the implementation of sympathetic cooling of molecular ions in surface-electrode traps and discuss possible challenges for the realization of such experiments.
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Affiliation(s)
- I M Georgescu
- Department of Chemistry, University of Basel, Klingelbergstrasse 80, 4056 Basel, Switzerland
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40
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Bertsche B, Osterwalder A. Dynamics of individual rotational states in an electrostatic guide for neutral molecules. Phys Chem Chem Phys 2011; 13:18954-61. [PMID: 21897976 DOI: 10.1039/c1cp21277j] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
The guiding properties of individual rotational states of deuterated ammonia inside an electrostatic hexapole guide are presented. The guide is combined with resonance enhanced multiphoton ionization detection to assess the guiding probabilities and velocity distributions as a function of the rotational quantum numbers J and K. Due to the differences in the effective dipole moment these states are prepared at significantly different translational temperatures. A model is presented that describes the velocity-distribution for individual M-sublevels, and this model is also used to determine a rotational-state dependent translational temperature. Furthermore, the hexapole field has been replaced by a dipole field in order to obtain a band-pass velocity filter. However, the resulting change in the final velocity distribution is similar to that obtained from a hexapole guide but with increased backing pressure, leading to collisional acceleration of the slow molecules.
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Affiliation(s)
- Benjamin Bertsche
- Institute of Chemical Sciences and Engineering, Ecole Polytechnique Fédérale de Lausanne, Switzerland
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41
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Gingell AD, Bell MT, Oldham JM, Softley TP, Harvey JN. Cold chemistry with electronically excited Ca+ Coulomb crystals. J Chem Phys 2011; 133:194302. [PMID: 21090857 DOI: 10.1063/1.3505142] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Rate constants for chemical reactions of laser-cooled Ca(+) ions and neutral polar molecules (CH(3)F, CH(2)F(2), or CH(3)Cl) have been measured at low collision energies (<E(coll)>/k(B)=5-243 K). Low kinetic energy ensembles of (40)Ca(+) ions are prepared through Doppler laser cooling to form "Coulomb crystals" in which the ions form a latticelike arrangement in the trapping potential. The trapped ions react with translationally cold beams of polar molecules produced by a quadrupole guide velocity selector or with room-temperature gas admitted into the vacuum chamber. Imaging of the Ca(+) ion fluorescence allows the progress of the reaction to be monitored. Product ions are sympathetically cooled into the crystal structure and are unambiguously identified through resonance-excitation mass spectrometry using just two trapped ions. Variations of the laser-cooling parameters are shown to result in different steady-state populations of the electronic states of (40)Ca(+) involved in the laser-cooling cycle, and these are modeled by solving the optical Bloch equations for the eight-level system. Systematic variation of the steady-state populations over a series of reaction experiments allows the extraction of bimolecular rate constants for reactions of the ground state ((2)S(1/2)) and the combined excited states ((2)D(3/2) and (2)P(1/2)) of (40)Ca(+). These results are analyzed in the context of capture theories and ab initio electronic structure calculations of the reaction profiles. In each case, suppression of the ground state rate constant is explained by the presence of a submerged or real barrier on the ground state potential surface. Rate constants for the excited states are generally found to be in line with capture theories.
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Affiliation(s)
- Alexander D Gingell
- Department of Chemistry, University of Oxford, Chemistry Research Laboratory, Oxford OX1 3TA, United Kingdom
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42
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Tacconi M, Gianturco FA, Belyaev AK. Computing charge-exchange cross sections for Ca+ collisions with Rb at low and ultralow energies. Phys Chem Chem Phys 2011; 13:19156-64. [DOI: 10.1039/c1cp20916g] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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43
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Doherty WG, Bell MT, Softley TP, Rowland A, Wrede E, Carty D. Production of cold bromine atoms at zero mean velocity by photodissociation. Phys Chem Chem Phys 2011; 13:8441-7. [DOI: 10.1039/c0cp02472d] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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44
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Liu Y, Yun M, Xia Y, Deng L, Yin J. Experimental generation of a cw cold CH3CN molecular beam by a low-pass energy filtering. Phys Chem Chem Phys 2010; 12:745-52. [DOI: 10.1039/b913929j] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
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45
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Gianturco FA, Tacconi M. Concluding remarks: achievements and challenges in cold and ultracold molecules. Faraday Discuss 2009; 142:463-77. [DOI: 10.1039/b910178k] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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