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State-Resolved Mutual Neutralization Experiments on Atomic Hydrogen Anions: H- with Li+, O+, N+, and C+
Stockholm University, Faculty of Science, Department of Physics.ORCID iD: 0000-0002-4437-3138
2024 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis presents experimental studies of mutual-neutralization reactions between H- and the cations 7Li+, 16O+, 12C+ and 14N+ at the double electrostatic ion-beam storage ring DESIREE. By overlapping two keV ion beams, with corresponding speeds of ca. 1000 km/s, and matching their velocities with applied electric fields, the center-of-mass collision energies are reduced to a few tens of meV. Time- and position-sensitive detectors allow the measurement of the  separation of the two formed neutral products, which depends on the kinetic-energy release in the charge-transfer reaction. The branching fractions into the different quantum states are extracted by binning or modelling of the measured product-separation distributions.

Due to the difficulty of merged-beams experiments with high mass ratio between the ions, 1H- is often replaced with 2H-. We were able to merge beams with a mass ratio of up to 16 between the ions, which allowed us to use 1H- in all studies presented here. For H-+7Li+ and H-+16O+, we included both hydrogen isotopes, and found a significant isotope effect. The lighter hydrogen isotope leads to an increased population in lower excited states in both cases.

Our data constitute important benchmarks for theoretical calculations that are needed in the modelling of stellar photospheres.We compare our experimental findings to different theoretical models and discuss their strengths and shortcomings.

In order to achieve these scientific results, the thesis work involved the development of data preparation and analysis for a frame- and an event-based detector, as well as the development of experimental methods.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University , 2024. , p. 58
Keywords [en]
merged beams, ion, event-based, neutralization, charge transfer, stellar photosphere, non-LTE, TPX3CAM
National Category
Atom and Molecular Physics and Optics
Research subject
Chemical Physics
Identifiers
URN: urn:nbn:se:su:diva-229120ISBN: 978-91-8014-831-3 (print)ISBN: 978-91-8014-832-0 (electronic)OAI: oai:DiVA.org:su-229120DiVA, id: diva2:1857691
Public defence
2024-08-30, Pärlan, hus 1, plan 6, Albano, Albanovägen 18 and online via Zoom, public link is available at the department website, Stockholm, 13:00 (English)
Opponent
Supervisors
Funder
Knut and Alice Wallenberg Foundation, 2018.0028Available from: 2024-06-04 Created: 2024-05-14 Last updated: 2024-05-29Bibliographically approved
List of papers
1. Observation of an isotope effect in state-selective mutual neutralization of lithium with hydrogen
Open this publication in new window or tab >>Observation of an isotope effect in state-selective mutual neutralization of lithium with hydrogen
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2023 (English)In: Physical Review A: covering atomic, molecular, and optical physics and quantum information, ISSN 2469-9926, E-ISSN 2469-9934, Vol. 108, no 4, article id 042810Article in journal (Refereed) Published
Abstract [en]

We report on mutual neutralization measurements between 7Li+ and 1H- at effective center-of-mass collision energies in the range of 100 to 350 meV. We find that final states of lithium with principal quantum number n = 3 dominate with 3s separated from the unresolved 3p and 3d states. We measure the 3s branching fraction to be 0.665(12) at 100(16) meV and no significant dependence on collision energy is observed in the studied range. Comparing to previous results on mutual neutralization between 7Li+ and 2H- [G. Eklund et al., Phys. Rev. A 102, 012823 (2020)], we find that 7Li+ collisions with 1H- result in a significantly higher 3s branching fraction than collisions with 2H-. The difference is 0.087(14). The 3s branching fraction of 7Li+ + 1H- and the determined isotope difference are in agreement with results from extended full quantum calculations based on the same input data and numerical method as in Croft et al. [H. Croft, A. S. Dickinson, and F. X. Gadea, J. Phys. B 32, 81 (1999)]. These calculations reveal strong Stueckelberg oscillations of the 3s branching fraction for both isotopes.

National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:su:diva-223888 (URN)10.1103/PhysRevA.108.042810 (DOI)001089119300011 ()2-s2.0-85176454030 (Scopus ID)
Available from: 2023-11-21 Created: 2023-11-21 Last updated: 2024-05-14Bibliographically approved
2. State-resolved mutual neutralization of 16O+ with 1H and 2H at collision energies below 100 meV
Open this publication in new window or tab >>State-resolved mutual neutralization of 16O+ with 1H and 2H at collision energies below 100 meV
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2024 (English)In: Physical Review A: covering atomic, molecular, and optical physics and quantum information, ISSN 2469-9926, E-ISSN 2469-9934, Vol. 109, no 5, article id 052820Article in journal (Refereed) Published
Abstract [en]

We measured the product-state distribution and its dependence on the hydrogen isotope for the mutual neutralization between 16O+ and 1,2H at the double electrostatic ion-beam storage ring DESIREE for center-of-mass collision energies below 100 meV. We find at least six product channels into ground-state hydrogen and oxygen in different excited states. The majority of oxygen products populate terms corresponding to 2⁢𝑠22⁢𝑝3⁢(4𝑆)⁢4⁢𝑠 with 5S as the main reaction product. We also observe product channels into terms corresponding to 2⁢𝑠22⁢𝑝3⁢(4𝑆)⁢3⁢𝑝. Collisions with the heavier hydrogen isotope yield a branching into these lower excited states smaller than collisions with 1H. The observed reaction products agree with the theoretical predictions. The detailed branching fractions, however, differ between the theoretical results, and none of them fully agree with the experiment.

National Category
Atom and Molecular Physics and Optics
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-229115 (URN)10.1103/PhysRevA.109.052820 (DOI)
Available from: 2024-05-13 Created: 2024-05-13 Last updated: 2024-05-23Bibliographically approved
3. State-resolved  mutual neutralization of carbon and nitrogen cations with hydrogen anions at sub-eV collision energies
Open this publication in new window or tab >>State-resolved  mutual neutralization of carbon and nitrogen cations with hydrogen anions at sub-eV collision energies
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(English)Manuscript (preprint) (Other academic)
National Category
Atom and Molecular Physics and Optics
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-229124 (URN)
Available from: 2024-05-13 Created: 2024-05-13 Last updated: 2024-05-14

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Schmidt-May, Alice Frederike

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