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Electron transfer and fragmentation in fullerene collisions
Stockholm University, Faculty of Science, Department of Physics.
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis, we present results from detailed gas phase studies of intrinsic properties of fullerenes (C60) and clusters of fullerenes as probed by slow multiply charged (atomic or cluster) ions in combination with coincidence time-of-flight mass spectrometry. We have investigated the structures, stabilities, and the electron mobilities of multiply charged clusters of fullerenes, (C60)nr+ (r=2-5). We found that the (C60)nr+ cluster ions are weakly bound by van der Waals forces and the electric conductivity is high in strong contrast to the typical characteristics of other van der Waals type clusters and fullerene crystals (fullerite), where the charge is strongly localized. The high charge mobility was rationalized within the framework of a novel classical static over-the-barrier model for two conducting spheres used to describe multiple charge transfer processes between two neighboring fullerenes in the cluster. The model results showed that electron transfer is possible as soon as the C60-C60 system is charged, consistent with earlier experimental results from slow C60q+ + C60 collisions where an electric contact is established (during the very short interaction time of the collision) between the two molecules at distances outside the binding distance in the C60-C60 system. The present electrostatic model was also used to guide the interpretation of the measured kinetic energy releases in the fragmentation of multiply charged dimers, (C60)2r+ → C60r1+ + C60r2+.

In like manner, we have measured kinetic energy releases in the break-ups of multiply charged monomer fullerene ions with the aid of fragment-ion momentum spectroscopy. This yielded an excellent platform for investigations of the projectile and target dependencies on various intrinsic features such as the ultimate Coulomb stability limits for C60r+ and C70r+ ions, competition between different reaction pathways, and multi-fragmentation processes. The experimental results for the stability limits for multiply charged fullerenes are discussed in view of recent high level Density Functional Theory calculations of C60r+ → C58(r-1)+ + C2+ transition states and our electrostatic model.

The Density Functional Theory results are also used to check the validity and limitations of the classical model regarding the description of fragmentation processes, while a comparison with advanced molecular dynamic calculations of Ar8++Na40 collisions were made for investigating its applicability for charge transfer processes. We found that the present model indeed is useful for describing main features in inherent complex molecular processes at sufficiently low collision velocities. In addition, we propose an extension of the present model to consider two dielectric spheres immersed in a dielectric medium, which might be applied also outside the cluster research field.

Place, publisher, year, edition, pages
Stockholm: Fysikum , 2005. , 121 p.
Keyword [en]
fullerene
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:su:diva-630ISBN: 91-7155-118-2 (print)OAI: oai:DiVA.org:su-630DiVA: diva2:196318
Public defence
2005-09-23, sal FB42, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 09:30
Opponent
Supervisors
Available from: 2005-09-01 Created: 2005-09-01Bibliographically approved
List of papers
1. Fragmentation and ionization of C70 and C60 by slow ions of intermediate charge
Open this publication in new window or tab >>Fragmentation and ionization of C70 and C60 by slow ions of intermediate charge
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2006 (English)In: European Physical Journal D: Atomic, Molecular and Optical Physics, ISSN 1434-6060, E-ISSN 1434-6079, Vol. 38, no 2, 299-306 p.Article in journal (Refereed) Published
Abstract [en]

We have measured total and coincident (with outgoing charge-state analyzed projectiles) ionization and fragmentation spectra of C60 and C70 following collisions with Xe4+ and Kr4+ at v = 0.06 a.u. Intact positive fullerene ions in charge states up to five (C605+ and C705+) are produced with both projectiles and for Kr4++C70 collisions we even observe a small C706+ peak. The C60/70-2m3+ (m=1–7) intensity distributions are predominantly associated with the stabilization of three electrons on the projectile (s=3) and are significantly different for Xe4+- and Kr4+-projectiles. On the other hand, we find remarkable similarities in the C3+-C11+ multi-fragmentation pattern regardless of projectile species (mass) although they are associated with closer encounters in which the projectile is fully neutralized (s=4). Simple Monte Carlo calculations of nuclear and electronic loss processes show that both these contributions are very similar in glancing Xe4++C60 and Kr4++C60 collisions, suggesting that frontal (and more violent) collisions are strongly suppressed under the present experimental conditions. Nevertheless it is surprising that the more distant collisions (s=3) are projectile mass dependent, while the closer collisions (s=4) are not. This indicates that this simple approach (although it reproduces more advanced quantum mechanical calculations for slow collisions with singly charged atomic ions rather well) is not valid for a comprehensive description of the energy transfer processes in the present collision systems involving projectiles of higher charge states.

Place, publisher, year, edition, pages
Springer, 2006
Keyword
34.70.+e Charge transfer - 36.40.Qv Stability and fragmentation of clusters - 36.40.Wa Charged clusters
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:su:diva-24003 (URN)10.1140/epjd/e2006-00005-7 (DOI)
Note
Part of urn:nbn:se:su:diva-630Available from: 2005-09-01 Created: 2005-09-01 Last updated: 2010-12-01Bibliographically approved
2. Ionization of C70 and C60 molecules by slow highly charged ions: A comparison
Open this publication in new window or tab >>Ionization of C70 and C60 molecules by slow highly charged ions: A comparison
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2004 In: Physical Review A, Vol. 69, 053203- p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:su:diva-24004 (URN)
Note
Part of urn:nbn:se:su:diva-630Available from: 2005-09-01 Created: 2005-09-01Bibliographically approved
3. Electrostatic model calculations of fission barriers for fullerene ions
Open this publication in new window or tab >>Electrostatic model calculations of fission barriers for fullerene ions
2004 In: European Physical Journal D, ISSN 1434-6060, Vol. 29, 63- p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:su:diva-24005 (URN)
Note
Part of urn:nbn:se:su:diva-630Available from: 2005-09-01 Created: 2005-09-01Bibliographically approved
4. Highly Charged Clusters of Fullerenes: Charge Mobility and Appearance Sizes
Open this publication in new window or tab >>Highly Charged Clusters of Fullerenes: Charge Mobility and Appearance Sizes
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2003 In: Physical Review Letters, Vol. 91, no 21, 215504- p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:su:diva-24006 (URN)
Note
Part of urn:nbn:se:su:diva-630Available from: 2005-09-01 Created: 2005-09-01Bibliographically approved
5. Barriers for asymmetric fission of multiply charged C60 fullerenes
Open this publication in new window or tab >>Barriers for asymmetric fission of multiply charged C60 fullerenes
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2003 In: Physical Review A, Vol. 67, 062719- p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:su:diva-24007 (URN)
Note
Part of urn:nbn:se:su:diva-630Available from: 2005-09-01 Created: 2005-09-01Bibliographically approved
6. Energy releases in the fission of multiply charged C60 ions
Open this publication in new window or tab >>Energy releases in the fission of multiply charged C60 ions
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2003 In: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Vol. 205, 643- p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:su:diva-24008 (URN)
Note
Part of urn:nbn:se:su:diva-630Available from: 2005-09-01 Created: 2005-09-01Bibliographically approved
7. Static over-the-barrier model for electron transfer between metallic spherical objects
Open this publication in new window or tab >>Static over-the-barrier model for electron transfer between metallic spherical objects
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2002 In: Physical Review A, Vol. 66, 032710- p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:su:diva-24009 (URN)
Note
Part of urn:nbn:se:su:diva-630Available from: 2005-09-01 Created: 2005-09-01Bibliographically approved

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