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Heavy particle interference and diffraction in fast electron transfer collisions
Stockholm University, Faculty of Science, Department of Physics.
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis presents experimental results from the synchrotron cooler and storage ring CRYRING on charge transfer processes in fast electron transfer collisions using high-resolution cold target recoil-ion momentum spectroscopy. The main focus of these studies was to investigate a key concept of quantum mechanics: the wave-particle duality. One series of experiments has been dedicated to the study of heavy particle de Broglie wave interference due to scattering on a molecular ’double slit’. This is a fundamental manifestation of the wave properties of matter. Quantum interference oscillations were observed in the target orientation dependent cross section of single- and double-electron capture from H2 to 1.3 MeV protons and to 1.2 and 2.0 MeV He2+ ions. Another study, included in this work, is a series of angular differential cross section measurements for single-electron capture to 1.3-12.5 MeV kinetic energy protons from He that enabled us to systematically investigate the classically allowed non-radiative electron capture process in fast collisions predicted by L. H. Thomas in 1927. The cross section for this process is expected to have a nonrelativistic, asymptotic dependence on the projectile velocity, vp, of vp11. This prediction (from 1927) was verified experimentally for the first time through the present measurements. Using the above mentioned experimental data in addition to measurements of double electron capture by 6.0 MeV He2+ from He, we have also studied the dominating, central part of the angular differential cross section, /, where the peak shapes and widths surprisingly are very similar regardless of projectile energy and the number of captured electrons. We explain this with a diffraction model for the electron capture and calculate the corresponding diffracting electron capture ‘apertures’ from the shapes and widths of the measured cross sections and the projectile de Broglie wavelengths. We have on one hand established very strong experimental support for the picture suggested by Thomas in 1927 in which electrons and protons are described as classical particles. On the other hand, the diffraction picture describes the shapes of the central peaks in /dΩ quite well, and nicely explains appearances of second and a third maxima in the angular differential cross section. It is hard to see how these seemingly contradicting results can be explained through complementary classical and quantum descriptions of the same underlying physical processes.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University , 2011. , 77 p.
National Category
Physical Sciences
Research subject
Physics
Identifiers
URN: urn:nbn:se:su:diva-57190ISBN: 978-91-7447-315-5OAI: oai:DiVA.org:su-57190DiVA: diva2:414554
Public defence
2011-06-03, sal FB42, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 13:00 (English)
Opponent
Supervisors
Note
At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 3: Manuscript. Available from: 2011-05-12 Created: 2011-05-03 Last updated: 2011-05-06Bibliographically approved
List of papers
1. Evidence of Wave-Particle Duality for Single Fast Hydrogen Atoms
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2008 (English)In: Physical Review Letters, ISSN 0031-9007, Vol. 101, no 8, 083201- p.Article in journal (Refereed) Published
Abstract [en]

We report the direct observation of interference effects in a Young's double-slit experiment where the interfering waves are two spatially separated components of the de Broglie wave of single 1.3 MeV hydrogen atoms formed close to either target nucleus in H+ + H2 electron-transfer collisions. Quantum interference strongly influences the results even though the hydrogen atoms have a de Broglie wavelength, \lambda_dB, as small as 25 fm.

National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:su:diva-15947 (URN)10.1103/PhysRevLett.101.083201 (DOI)000258643600021 ()
Available from: 2008-12-11 Created: 2008-12-11 Last updated: 2011-12-27Bibliographically approved
2. Two-Center Double-Capture Interference in Fast He2++H2 Collisions
Open this publication in new window or tab >>Two-Center Double-Capture Interference in Fast He2++H2 Collisions
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2009 (English)In: Physical Review Letters, ISSN 0031-9007, Vol. 102, no 15, 153201- p.Article in journal (Refereed) Published
Abstract [en]

We report the first observation of Young-type interference effects in a two-electron transfer process. These effects change strongly as the projectile velocity changes in fast (1.2 and 2.0 MeV) He^{2+}-H_2 collisions as manifested in strong variations of the double-electron capture rates with the H_2 orientation. This is consistent with fully quantum mechanical calculations, which ignore sequential electron transfer, and a simple projectile de Broglie wave picture assuming that two-electron transfer probabilities are higher in collisions where the projectile passes close to either one of the H_2 nuclei.

National Category
Atom and Molecular Physics and Optics
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-33279 (URN)10.1103/PhysRevLett.102.153201 (DOI)000265285700025 ()
Available from: 2009-12-22 Created: 2009-12-22 Last updated: 2011-12-27Bibliographically approved
3. Orientation-dependent charge transfer cross section in 1.04MeV p-N2 collisions
Open this publication in new window or tab >>Orientation-dependent charge transfer cross section in 1.04MeV p-N2 collisions
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(English)Manuscript (preprint) (Other academic)
National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-57195 (URN)
Available from: 2011-05-03 Created: 2011-05-03 Last updated: 2011-12-27Bibliographically approved
4. Importance of Thomas single-electron transfer in fast p-He collisions
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2010 (English)In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 81, no 1, 12714- p.Article in journal (Refereed) Published
Abstract [en]

We report experimental angular differential cross sections for nonradiative single-electron capture in p-He collisions (p + He -> H + He+) with a separate peak at the 0.47 mrad Thomas scattering angle for energies in the 1.3-12.5 MeV range. We find that the intensity of this peak scales with the projectile velocity as v(P)(-11). This constitutes the first experimental test of the prediction from 1927 by L. H. Thomas [Proc. R. Soc. 114, 561 (1927)]. At our highest energy, the peak at the Thomas angle contributes with 13.5% to the total integrated nonradiative single-electron capture cross section.

National Category
Natural Sciences
Identifiers
urn:nbn:se:su:diva-49677 (URN)10.1103/PhysRevA.81.012714 (DOI)000277958100023 ()
Note
authorCount :12Available from: 2010-12-17 Created: 2010-12-17 Last updated: 2011-12-27Bibliographically approved
5. Angular scattering in fast ion-atom electron transfer collisions: projectile wave diffraction and Thomas mechanisms
Open this publication in new window or tab >>Angular scattering in fast ion-atom electron transfer collisions: projectile wave diffraction and Thomas mechanisms
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2010 (English)In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 43, no 18, 185209- p.Article in journal (Refereed) Published
Abstract [en]

We report experimental angular differential cross sections for double-electron capture in He2+ + He collisions and single-electron capture in H+ + He collisions for the 1.3-12.5 MeV kinetic energy range. In all cases, the total cross sections are dominated by forward scattering peaks in d sigma/d Omega. The shapes and widths (but not the magnitudes) of these peaks are very similar for all energies and for capture of one or two electrons corresponding also to our measured linear increases in the transverse momentum transfers with increasing projectile velocities. These observations may be ascribed to diffraction limitations which are connected to electron transfer probabilities P(b) which are significant in limited regions of b only. For the H+ + He single-electron capture we observe two additional maxima in the angular differential cross sections. We conclude that while the secondary maxima at similar to 0.5 mrad probably have large contributions from the Thomas proton-electron-nucleus scattering mechanism, the third maxima at similar to 0.75 mrad are most likely mainly due to projectile de Broglie wave diffraction.

National Category
Natural Sciences
Identifiers
urn:nbn:se:su:diva-50326 (URN)10.1088/0953-4075/43/18/185209 (DOI)000281530700013 ()
Note
authorCount :12Available from: 2010-12-22 Created: 2010-12-22 Last updated: 2011-12-27Bibliographically approved

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