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Theoretical studies of chemical dynamics on excited states, driven by non-adiabatic effects: Charge recombination reactions
Stockholm University, Faculty of Science, Department of Physics. (Chemical Physics)
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis is based on theoretical studies of molecular collisions occurring at relatively low to intermediate collision energies. The collisions are called dissociative recombination (DR) and mutual neutralization (MN). In a molecular quantum mechanical picture, both reactions involve many highly excited molecular electronic states that are interacting by non-adiabatic couplings with each other. The molecular complexes involved in the collisions are relatively (diatomic or triatomic systems) composed of relative light atoms. This allows for accurate quantum chemistry calculations and a quantum mechanical description of the nuclear motions. The reactions studied here are the MN reaction in collisions of H++ H-, Li++ F-, and He++ H- and the DR reaction of H2O+. Rotational couplings are investigated in the study of MN reaction for  He++ H . For some reactions, the electronic resonant states have to be considered. These are not bound states, but are states interacting with the ionization continuum. Electronic structure calculations are combined with electron scattering calculations to accurately compute potential energy curves for the resonant states involved in the DR of H2O+ and the MN of  He++ H. From these calculations, the autoionization widths of the resonant states are also obtained. Once the potential energy curves are computed for the systems, the nuclear dynamics are studied either semi-classically, using the Landau-Zener method or quantum mechanically, employing the time-independent and time-dependant Schrödinger equations. Reaction cross section and final states distribution are computed for all the reactions, showing significantly large cross section at low to intermediate collision energies. For the MN processes, studied here, not only total cross sections are calculated but differential cross sections as well. Where possible, comparisons with previous experimental and theoretical results are performed

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University , 2016. , 88 p.
Keyword [en]
Mutual neutralization, Dissociative recombination, electronic structure, non-adiabatic
National Category
Atom and Molecular Physics and Optics
Research subject
Theoretical Physics
Identifiers
URN: urn:nbn:se:su:diva-128723ISBN: 978-91-7649-409-7 (print)OAI: oai:DiVA.org:su-128723DiVA: diva2:916219
Public defence
2016-05-23, sal, FA32, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Manuscript.

Available from: 2016-04-30 Created: 2016-04-01 Last updated: 2017-02-23Bibliographically approved
List of papers
1. Landau-Zener studies of mutual neutralization in collisions of H+ + H- and Be+ + H-
Open this publication in new window or tab >>Landau-Zener studies of mutual neutralization in collisions of H+ + H- and Be+ + H-
2014 (English)In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 47, no 22, 225206Article in journal (Refereed) Published
Abstract [en]

Semi-classical Landau-Zener studies of mutual neutralization reactions in low-energy H+ + H- and Be+ + H- collisions are performed. Avoided crossings between ionic and covalent states occurring at large internuclear distances are considered, and electronic couplings between these states are estimated using different semi-empirical and ab initio methods and tested on the H+ + H- reaction. The method is then applied to compute the cross sections and final state distributions for mutual neutralization in collisions of H- with Be+. These are reactions that might be important for the modeling of the fusion edge plasma of the divertor of ITER.

Keyword
mutual neutralization, Landau-Zener, semi-classical, charged transfer
National Category
Physical Sciences
Research subject
Theoretical Physics
Identifiers
urn:nbn:se:su:diva-110746 (URN)10.1088/0953-4075/47/22/225206 (DOI)000344499200011 ()
Note

AuthorCount:3;

Available from: 2014-12-18 Created: 2014-12-17 Last updated: 2017-12-05Bibliographically approved
2. Mutual neutralization in collisions of Li+ and F-
Open this publication in new window or tab >>Mutual neutralization in collisions of Li+ and F-
2015 (English)In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 462, 23-27 p.Article in journal (Refereed) Published
Abstract [en]

Mutual neutralization in collisions of Li+ and F is driven by an avoided crossing between the two lowest (1)Sigma(+) electronic states of the LiF system. These electronic states are computed using the multi-reference configuration interaction method. We investigate how the adiabatic potential energy curves and the non-adiabatic coupling element depend on the choice of the reference configurations as well as the basis set. Using diabatic states, the total and differential cross sections for mutual neutralization are computed.

Keyword
Mutual neutralization, Non-adiabatic, Configuration interaction, LiF
National Category
Chemical Sciences Physical Sciences
Research subject
Theoretical Physics
Identifiers
urn:nbn:se:su:diva-124738 (URN)10.1016/j.chemphys.2015.08.006 (DOI)000365034300005 ()
Available from: 2016-01-10 Created: 2016-01-04 Last updated: 2017-12-01Bibliographically approved
3. Studies of HeH: DR, RIP, VE, DE, PI, MN, ...
Open this publication in new window or tab >>Studies of HeH: DR, RIP, VE, DE, PI, MN, ...
Show others...
2015 (English)In: EPJ Web of Conferences, ISSN 2101-6275, E-ISSN 2100-014X, Vol. 84, 03001Article in journal (Refereed) Published
Abstract [en]

The resonant states of HeH are computed by combining structure calculations at a full configuration interaction level with electron scattering calculations carried out using the Complex-Kohn variational method. We obtain the potential energy curves, autoionization widths, as well as non-adiabatic couplings among the resonant states. Using the non-adiabatic couplings, the adiabatic to diabatic transformation matrix can be obtained. A strict diabatization of the resonant states will be used to study various scattering processes where the resonant states are involved. These processes involve high energy dissociative recombination (DR) and ion-pair formation (RIP), resonant and direct dissociative excitation (DE), penning ionization (PI) as well as mutual neutralization (MN).

National Category
Physical Sciences Chemical Sciences
Research subject
Theoretical Physics
Identifiers
urn:nbn:se:su:diva-117059 (URN)10.1051/epjconf/20158403001 (DOI)000351835100008 ()
Conference
9th International Conference on Dissociative Recombination: Theory, Experiment, and Applications, July 07-12, 2013, Paris, France
Note

AuthorCount:5;

Available from: 2015-05-11 Created: 2015-05-06 Last updated: 2017-12-04Bibliographically approved
4. A theoretical study of mutual neutralization of He++H- collisions
Open this publication in new window or tab >>A theoretical study of mutual neutralization of He++H- collisions
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Total and differential cross sections for mutual neutralization in low energy (0.001 eV -100 eV) He + and H − collisions are calculated ab initio and fully quantum mechanically. Atomic final state distributions and isotope effects are investigated. The theoretical model includes dynamics on eleven coupled states of 2 Σ + symmetry where autoionization is incorporated. The potential energy curves, autoionization widths and non-adiabatic couplings of electronic resonant states of HeH are computed by combining structure calculations with electron scattering calculations. The nuclear dynamics is studied using a strict diabatic representation of the resonant states. Effects of rotational couplings between 2 Σ + and 2 Π electronic states are investigated in the pure precession approximation.

National Category
Atom and Molecular Physics and Optics
Research subject
Theoretical Physics
Identifiers
urn:nbn:se:su:diva-128800 (URN)
Available from: 2016-04-04 Created: 2016-04-04 Last updated: 2016-04-11Bibliographically approved
5. Differential and total cross sections of mutual neutralization in low-energy collisions of isotopes of H+ + H-
Open this publication in new window or tab >>Differential and total cross sections of mutual neutralization in low-energy collisions of isotopes of H+ + H-
Show others...
2016 (English)In: Physical Review A, ISSN 2469-9926, Vol. 93, no 3, 032701Article in journal (Refereed) Published
Abstract [en]

Mutual neutralization in the collisions of H+ and H- is studied both theoretically and experimentally. The quantum-mechanical ab initio model includes covalent states associated with the H(1)+H(n <= 3) limits and the collision energy ranges from 1 meV to 100 eV. The reaction is theoretically studied for collisions between different isotopes of the hydrogen ions. From the partial wave scattering amplitude, the differential and total cross sections are computed. The differential cross section is analyzed in terms of forward- and backward-scattering events, showing a dominance of backward scattering which can be understood by examining the phase of the scattering amplitudes for the gerade and ungerade set of states. The isotope dependence of the total cross section is compared with the one obtained using a semiclassical multistate Landau-Zener model. The final state distribution analysis emphasizes the dominance of the n = 3 channel for collisions below 10 eV, while at higher collision energies, the n = 2 channel starts to become important. For collisions of ions forming a molecular system with a larger reduced mass, the n = 2 channel starts to dominate at lower energies. Using a merged ion-beam apparatus, the branching ratios for mutual neutralization in H+ and H- collisions in the energy range from 11 to 185 eV are measured with position- and time-sensitive particle detectors. The measured and calculated branching ratios satisfactorily agree with respect to state contributions.

National Category
Physical Sciences
Research subject
Theoretical Physics
Identifiers
urn:nbn:se:su:diva-128507 (URN)10.1103/PhysRevA.93.032701 (DOI)000371390900003 ()
Available from: 2016-04-11 Created: 2016-03-30 Last updated: 2016-04-11Bibliographically approved
6. Theoretical study of the mechanism of H2O+ dissociative recombination
Open this publication in new window or tab >>Theoretical study of the mechanism of H2O+ dissociative recombination
2015 (English)In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 92, no 1, 012708Article in journal (Refereed) Published
Abstract [en]

By combining electronic structure and scattering calculations, quasidiabatic potential energy surfaces of both bound Rydberg and electronic resonant states of the water molecule are calculated at the multireference configuration-interaction level. The scattering matrix calculated at low collision energy is used to obtain explicitly all couplings elements responsible for the electronic capture to bound Rydberg states. These are used to estimate the cross section arising from the indirect mechanism of dissociative recombination. Additionally, the role of the direct capture and dissociation through the resonant states is explored using wave-packet propagation along one-dimensional slices of the multidimensional potential energy surfaces.

National Category
Physical Sciences
Research subject
Theoretical Physics
Identifiers
urn:nbn:se:su:diva-120076 (URN)10.1103/PhysRevA.92.012708 (DOI)000358839200004 ()
Available from: 2015-09-07 Created: 2015-09-01 Last updated: 2017-12-04Bibliographically approved

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