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A unified model of reactive scattering processes: Application to the H2 reaction complex
Stockholm University, Faculty of Science, Department of Physics.ORCID iD: 0000-0002-4291-2636
2024 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis, reactive scattering processes involving the H2 reaction complex are studied ab initio and fully quantum mechanically. These processes have in common that they involve highly excited electronic states, which could be either bound or resonant. Non-adiabatic couplings, which can be significant both at small and large internuclear distances, need to be included to account for the interaction between the bound electronic states. In addition, the electronic resonant states interact with the ionization continuum at small internuclear distances, which may cause the collision complex to autoionize. In this work, a model is developed which incorporates these different coupling mechanisms. By introducing a quasidiabatic model at small internuclear distances, resonant states and couplings to the ionization continuum are incorporated. The quasidiabatic model is combined with a strict diabatic description, which rigorously incorporates non-adiabatic couplings among the bound electronic states. Nuclear dynamics are solved for using a close-coupling approach in a strict diabatic representation, where a non-local complex potential is included to account for loss into the ionization continuum. With this model, various reactive scattering processes can systematically be studied using the same set of potential energy curves and couplings. The model is applied in studies of H++H- mutual neutralization, H(1s)+H(ns) and H++H- associative ionization as well as dissociative recombination and resonant ion-pair formation in electron collisions with HD+. Cross sections and branching ratios are compared with results from previous experiments and theoretical studies.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University , 2024. , p. 76
Keywords [en]
associative ionization, dissociative recombination, mutual neutralization, resonant ion-pair formation, non-adiabatic dynamics
National Category
Atom and Molecular Physics and Optics
Research subject
Theoretical Physics
Identifiers
URN: urn:nbn:se:su:diva-228804ISBN: 978-91-8014-823-8 (print)ISBN: 978-91-8014-824-5 (electronic)OAI: oai:DiVA.org:su-228804DiVA, id: diva2:1855016
Public defence
2024-08-23, sal FB42, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 13:00 (English)
Opponent
Supervisors
Available from: 2024-05-30 Created: 2024-04-29 Last updated: 2024-05-22Bibliographically approved
List of papers
1. Mutual neutralization in H++H collisions: An improved theoretical model
Open this publication in new window or tab >>Mutual neutralization in H++H collisions: An improved theoretical model
2022 (English)In: Physical Review A: covering atomic, molecular, and optical physics and quantum information, ISSN 2469-9926, E-ISSN 2469-9934, Vol. 106, no 6, article id 062821Article in journal (Refereed) Published
Abstract [en]

The total and differential cross sections of mutual neutralization in H++H collisions are calculated ab initio and fully quantum mechanically for energies between 0.001 and 600 eV. Effects which have not previously been considered in studies on mutual neutralization (MN) for this system, such as inclusion of rotational couplings and autoionization, are investigated. Adiabatic potential curves corresponding to the relevant states of 1Σ, 1Σ, 1Πg and 1Πu symmetries as well as radial and rotational nonadiabatic couplings are computed ab initio. A quasidiabatic model is developed and applied in order to investigate the importance of higher excited states as well as the inclusion of autoionization. Molecular data for the lowest electronic resonant state in each symmetry are obtained by performing electron scattering calculations. It is shown that rotational couplings cause a significant increase of the total MN cross section while autoionization plays a minor role as a loss mechanism. Additionally, a differential cross section is obtained that is symmetric around θ=90. This result is in disagreement with a previous theoretical calculation where it was found that the differential cross section is dominated by backwards scattering.

National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:su:diva-214346 (URN)10.1103/PhysRevA.106.062821 (DOI)000905057800011 ()2-s2.0-85146143031 (Scopus ID)
Available from: 2023-02-03 Created: 2023-02-03 Last updated: 2024-04-29Bibliographically approved
2. Associative ionization in collisions of H plus + H- and H(1s) + H(ns)
Open this publication in new window or tab >>Associative ionization in collisions of H plus + H- and H(1s) + H(ns)
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 5, article id 052811Article in journal (Refereed) Published
Abstract [en]

Associative ionization in collisions of H+ + H- as well as H(1s) + H(ns) with n = 2, 3, 4 is studied theoretically. Relevant adiabatic potential curves and nonadiabatic couplings are calculated ab initio and the autoionization from the lowest electronic resonant states in the 11+g/u and 31+g/u symmetries are considered. The cross sections are obtained by solving the coupled Schrodinger equation, including a complex potential matrix, in a strict diabatic representation. The importance of using a nonlocal description of autoionization is investigated. Associative ionization is also studied for different isotopes of hydrogen. Calculated cross sections are compared with results from measurements.

National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:su:diva-224664 (URN)10.1103/PhysRevA.108.052811 (DOI)001110834300011 ()2-s2.0-85177618381 (Scopus ID)
Available from: 2023-12-19 Created: 2023-12-19 Last updated: 2024-04-29Bibliographically approved
3. Dissociative recombination and resonant ion-pair formation in electron collisions with HD+
Open this publication in new window or tab >>Dissociative recombination and resonant ion-pair formation in electron collisions with HD+
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 052806Article in journal (Refereed) Published
Abstract [en]

We have developed a method for which a variety of reactive scattering processes involving the H2 reaction complex can be studied using the same set of potential curves and couplings. The method is based on a close coupling approach in a strict diabatic representation. By rigorously incorporating non-adiabatic couplings among bound states, we enable the computation of final state distributions. Loss into the ionization continuum is accounted for with a non-local complex potential matrix. The method has successfully been applied in the studies of H+ + H- mutual neutralization and H(1s) + H(ns) associative ionization. In this paper, we investigate the applicability of this method to dissociative recombination and resonant ion-pair formation in electron collisions with HD+. The importance of a non-local description of autoionization is demonstrated. Calculated cross sections and final state distributions are compared with results from experiments and previous theoretical studies.

Keywords
dissociative recombination, resonant ion-pair formation
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:su:diva-228796 (URN)10.1103/PhysRevA.109.052806 (DOI)001237594600002 ()2-s2.0-85192685609 (Scopus ID)
Available from: 2024-04-29 Created: 2024-04-29 Last updated: 2024-06-18Bibliographically approved
4. Treatment of asymptotic non-adiabatic couplings with higher order reprojection method in the diabatic representation
Open this publication in new window or tab >>Treatment of asymptotic non-adiabatic couplings with higher order reprojection method in the diabatic representation
Show others...
(English)Manuscript (preprint) (Other academic)
Abstract [en]

The problem of asymptotic non-adiabatic couplings in heavy particle collisions is treated using the reprojection method. The mixing matrix that mix the asymptotic solutions of the coupled states to obtain appropriate boundary conditions, is here derived to second order yielding a faster convergence of the cross section. Additionally, the reprojection method is implemented in a diabatic representation and applied to inelastic scattering of Li+Na, H+H and to mutual neutralization in H++H- collisions.

Keywords
reprojection method, asymptotic non-adiabatic couplings
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:su:diva-228797 (URN)
Available from: 2024-04-29 Created: 2024-04-29 Last updated: 2024-04-29

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