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Reaction dynamics on highly excited states
Stockholm University, Faculty of Science, Department of Physics. (Molecular Physics)
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis I have performed theoretical studies on the reaction dynamics in few-atom molecules. In particular, I have looked at reaction processes in which highly excited resonant states are involved. When highly excited states are formed, the dynamics becomes complicated and approximations normally used in chemical reaction studies are no longer applicable.To calculate the potential energy curve for some of these states as a function of internuclear distance, a combination of structure calculations and scattering calculations have to be performed, and the reaction dynamics on the potentials has been studied using both time-independent and time-dependent methods.The processes that have been studied and which are discussed in this thesis are ion-pair formation in electron recombination with H3+, dissociative recombination and ion-pair formation of HF+, mutual neutralization in H++F- collisions and dissociative recombination of BeH+. Isotope effects in these reactions have also been investigated. Our calculated cross sections are compared with experimentally measured cross sections for these reactions.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University , 2009. , 88 p.
Keyword [en]
ab initio calculations, dissociative recombination, resonant ion-pair formation, mutual neutralization, molecular electronic states, molecule-electron collisions, quantum chemistry, molecular dynamics
National Category
Atom and Molecular Physics and Optics Atom and Molecular Physics and Optics
Research subject
Chemical Physics
Identifiers
URN: urn:nbn:se:su:diva-27122ISBN: 978-91-7155-869-5 (print)OAI: oai:DiVA.org:su-27122DiVA: diva2:212693
Public defence
2009-06-01, sal FB52, AlbaNova universitetscentrum, Roslagstullsbacken 2, Stockholm, 10:00 (English)
Opponent
Supervisors
Available from: 2009-05-11 Created: 2009-04-23 Last updated: 2012-08-17Bibliographically approved
List of papers
1. Ion-pair formation in electron recombination with H3+
Open this publication in new window or tab >>Ion-pair formation in electron recombination with H3+
2006 (English)In: Philosophical Transactions. Series A: Mathematical, physical, and engineering science, ISSN 1364-503X, E-ISSN 1471-2962, Vol. 364, no 1848, 2999-3005 p.Article in journal (Refereed) Accepted
Abstract [en]

The process of resonant ion-pair formation following electron collisions with H3+ is studied. The relevant diabatic potential energy surfaces and the electronic couplings between these surfaces are calculated. The reaction is then described using a time-dependent approach with wave packets propagating on the coupled potentials. In order to describe the reaction, it is found necessary to include at least two dimensions in the model. The effects of the Rydberg states on the cross-section for this process are discussed.

Place, publisher, year, edition, pages
Royal Society Publishing, 2006
Keyword
Ion-pair state, wave packet dynamics
National Category
Atom and Molecular Physics and Optics Atom and Molecular Physics and Optics
Research subject
Chemical Physics
Identifiers
urn:nbn:se:su:diva-27087 (URN)10.1098/rsta.2006.1884 (DOI)
Available from: 2009-04-23 Created: 2009-04-22 Last updated: 2017-12-13Bibliographically approved
2. Electron collisions with H3+: Ion-pair formation
Open this publication in new window or tab >>Electron collisions with H3+: Ion-pair formation
2007 (English)In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 76, no 4, 042703-1-042703-9 p.Article in journal (Refereed) Published
Abstract [en]

The formation of the ion pair H2++H in electron recombination with H3+ is studied. The diabatic potentials and electronic couplings are extracted from ab initio electron scattering calculations as well as quantum chemistry calculations. In order to describe this reaction we include six coupled electronic states and propagate wave packets in two dimensions using the multiconfiguration time-dependent Hartree method. Also, the cross section for ion-pair formation in electron recombination with D3+ is calculated. The cross section for this isotopomer is found to be about a factor of 3 smaller than the cross section for H3+.

Place, publisher, year, edition, pages
The American Physical Society, 2007
Keyword
ab initio calculations, deuterium, hydrogen ions, ion recombination, isotope effects, molecular electronic states, molecule-electron collisions, positive ions, quantum chemistry
National Category
Atom and Molecular Physics and Optics Atom and Molecular Physics and Optics
Research subject
Chemical Physics
Identifiers
urn:nbn:se:su:diva-27106 (URN)10.1103/PhysRevA.76.042703 (DOI)
Available from: 2009-04-23 Created: 2009-04-22 Last updated: 2017-12-13Bibliographically approved
3. Dissociative recombination of HF+
Open this publication in new window or tab >>Dissociative recombination of HF+
2008 (English)In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 78, no 2, 022508-1-022508-12 p.Article in journal (Refereed) Published
Abstract [en]

The direct mechanism of dissociative recombination of HF+ is studied usingboth time-dependent and time-independent methods, where the dynamics on 30resonant states is explored. The relevant electronic states are calculatedab initio by combining electron scattering calculations with multireference configurationinteraction structure calculations. For collision energies between 0.04 and 10  eV,we obtain qualitative agreement with experiment. At 1.9  eV there isa sharp threshold in both the experimental and theoretical crosssections that can be explained by the opening of newasymptotic limits. The measured cross section below 0.04  eV is notreproduced due to the neglect of the electronic couplings betweenthe neutral states. We examine the validity of the localapproximation for treating autoionization from the resonant states included inthis study.

Place, publisher, year, edition, pages
The American Physical Society, 2008
Keyword
ab initio calculations, autoionisation, configuration interactions, dissociation, hydrogen compounds, ion recombination, molecule-electron collisions, resonant states
National Category
Atom and Molecular Physics and Optics Atom and Molecular Physics and Optics
Research subject
Chemical Physics
Identifiers
urn:nbn:se:su:diva-27107 (URN)10.1103/PhysRevA.78.022508 (DOI)000259263400081 ()
Available from: 2009-04-23 Created: 2009-04-22 Last updated: 2017-12-13Bibliographically approved
4. Resonant ion-pair formation in electron recombination with HF+
Open this publication in new window or tab >>Resonant ion-pair formation in electron recombination with HF+
(English)Manuscript (Other (popular science, discussion, etc.))
Abstract [en]

The cross section for resonant ion-pair formation in the collision of low-energy electrons with HF+ is calculated by the solution of the time-dependent Schrödinger equation with multiple coupledstates using a wave packet method. A diabatization procedure is proposed to obtain the electroniccouplings between quasidiabatic potentials of 1Σ+ symmetry for HF. By including these couplingsbetween the neutral states, the cross section for ion-pair formation increases with about two ordersof magnitude compared with the cross section for direct dissociation. Qualitative agreement with themeasured cross section is obtained. The oscillations in the calculated cross section are analyzed. Thecross section for ion-pair formation in electron recombination with DF+ is calculated to determinethe effect of isotopic substitution.

Keyword
ab initio calculations, autoionisation, configuration interactions, dissociation, hydrogen compounds, ion recombination, molecule-electron collisions, resonant states
National Category
Atom and Molecular Physics and Optics Atom and Molecular Physics and Optics
Research subject
Chemical Physics
Identifiers
urn:nbn:se:su:diva-27109 (URN)
Available from: 2009-04-23 Created: 2009-04-22 Last updated: 2010-01-14Bibliographically approved
5. Mutual neutralization in low-energy H(+) + F(-) collisions
Open this publication in new window or tab >>Mutual neutralization in low-energy H(+) + F(-) collisions
Show others...
2011 (English)In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 84, no 1, 012703- p.Article in journal (Refereed) Published
Abstract [en]

The cross section for mutual neutralization in collisions between H(+) and F(-) ions at low energies ( E <= 10 eV) is calculated using a molecular close-coupling approach. Two different representations of the quasidiabatic potentials and couplings of HF are used. The effect of autoionization on the cross section is investigated. The coupled Schrodinger equation for the nuclear motion is solved using a numerical integration of the corresponding matrix Riccati equation and the cross section for mutual neutralization is computed from the asymptotic value of the logarithmic derivative of the radial wave function. The magnitude of the cross section for mutual neutralization in this reaction is small compared to other systems. This can be understood by the lack of avoided crossings at large internuclear distances. Resonant structures are found in the cross section and these are assigned with dominant angular momentum quantum number. The cross section for mutual neutralization in collisions of D(+) and F(-) ions is also calculated.

National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-66584 (URN)10.1103/PhysRevA.84.012703 (DOI)000292690700007 ()
Note
authorCount :5Available from: 2011-12-21 Created: 2011-12-20 Last updated: 2017-12-08Bibliographically approved
6. Dissociative recombination of BeH+
Open this publication in new window or tab >>Dissociative recombination of BeH+
(English)Manuscript (Other academic)
Abstract [en]

The cross section for dissociative recombination of BeH+ is calculated by solution of the timedependent Schrödinger equation in the local complex potential approximation. The effects of couplings between resonant states and the Rydberg states converging to the ground state of the ionare studied. The relevant potentials, couplings and autoionization widths are extracted using abinitio electron scattering and structure calculations, followed by a diabatization procedure. Thecalculated cross sections shows a sizable magnitude at low energy, followed by a high-energy peakcentered around 1 eV. The electronic couplings between the neutral states induce oscillations in thecross section. Analytical forms for the cross sections at low collision energies are given.

Keyword
ab initio calculations, autoionisation, configuration interactions, dissociation, hydrogen compounds, ion recombination, molecule-electron collisions, resonant states
National Category
Atom and Molecular Physics and Optics Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:su:diva-27111 (URN)
Available from: 2009-04-23 Created: 2009-04-23 Last updated: 2010-01-14Bibliographically approved
7. Ion-pair formation in electron recombination with molecular ions
Open this publication in new window or tab >>Ion-pair formation in electron recombination with molecular ions
2007 (English)In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 88, 012065-1-012065-8 p.Article in journal (Refereed) Published
Abstract [en]

By studying ion-pair formation in electron recombination with molecular ions,fundamental knowledge on the molecular dynamics can be obtained. In order to study thesetypes of reactions, both the electron recombination as well as the dynamics all the way to theasymptotic limits must be well described. We have used the wave packet technique to studyion-pair formation in electron recombination with HeH+, HD+, H3+ and HF+. We here discusswhat will determine the general shape of the ion-pair cross section, the threshold effects, possibleinterference effects as well as the ratio of the cross sections of ion-pair formation to dissociativerecombination.

Place, publisher, year, edition, pages
IOP Publishing, 2007
Keyword
ab initio calculations, deuterium, hydrogen ions, ion recombination, molecular electronic states, molecule-electron collisions, positive ions, quantum chemistry
National Category
Atom and Molecular Physics and Optics Atom and Molecular Physics and Optics
Research subject
Chemical Physics
Identifiers
urn:nbn:se:su:diva-27113 (URN)10.1088/1742-6596/88/1/012065 (DOI)
Available from: 2009-04-23 Created: 2009-04-23 Last updated: 2017-12-13Bibliographically approved

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