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Collision Induced Fragmentation of Molecules and Molecular Clusters: Knockout Driven Reactions in Fullerenes and PAHs
Stockholm University, Faculty of Science, Department of Physics.
2014 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

This licentiate thesis covers experimental and theoretical studies of the fragmentation and sub- sequent reactions of fullerenes or Polycyclic Aromatic Hydrocarbons (PAHs). I present results from experiments where atoms or ions collide with fullerenes, PAHs, or clusters of these mole- cules at energies from 100 eV up to tens of keV.

The results of these experiments are interpreted using quantum chemical calculations, mol- ecular dynamics simulations, and a stopping model that we have developed. With these models I show that different energy transfer processes dominate at different collision energies, from nuclear stopping in low energy (~ 100 eV) collisions to electronic stopping at higher energies (~ 10 keV). I particularly focus on non-statistical fragmentation induced by nuclear stopping which can lead to the formation of exotic new species such as the odd-numbered C119 fullerene- like molecule. 

Place, publisher, year, edition, pages
Stockholm University, 2014.
National Category
Atom and Molecular Physics and Optics
Research subject
Physics
Identifiers
URN: urn:nbn:se:su:diva-103501OAI: oai:DiVA.org:su-103501DiVA: diva2:718723
Presentation
2014-06-13, FB53, Roslagstullbacken 21, Stockholm, 14:00 (English)
Opponent
Supervisors
Available from: 2014-07-01 Created: 2014-05-20 Last updated: 2014-07-01Bibliographically approved
List of papers
1. Formations of Dumbbell C-118 and C-119 inside Clusters of C-60 Molecules by Collision with alpha Particles
Open this publication in new window or tab >>Formations of Dumbbell C-118 and C-119 inside Clusters of C-60 Molecules by Collision with alpha Particles
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2013 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 110, no 18, 185501Article in journal (Refereed) Published
Abstract [en]

We report highly selective covalent bond modifications in collisions between keV alpha particles and van der Waals clusters of C-60 fullerenes. Surprisingly, C-119(+) and C-118(+) are the dominant molecular fusion products. We use molecular dynamics simulations to show that C-59(+) and C-58(+) ions-effectively produced in prompt knockout processes with He2+-react rapidly with C-60 to form dumbbell C-119(+) and C-118(+). Ion impact on molecular clusters in general is expected to lead to efficient secondary reactions of interest for astrophysics. These reactions are different from those induced by photons.

National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-91298 (URN)10.1103/PhysRevLett.110.185501 (DOI)000319019300008 ()
Funder
Swedish Research Council, 621-2008-3773, 621-2009-3468, 621-2011-4047EU, European Research Council, 246976
Note

AuthorCount:22;

Available from: 2013-06-27 Created: 2013-06-24 Last updated: 2017-12-06Bibliographically approved
2. Ions colliding with clusters of fullerenes-Decay pathways and covalent bond formations
Open this publication in new window or tab >>Ions colliding with clusters of fullerenes-Decay pathways and covalent bond formations
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2013 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 139, no 3, 034309Article in journal (Refereed) Published
Abstract [en]

We report experimental results for the ionization and fragmentation of weakly bound van der Waals clusters of n C-60 molecules following collisions with Ar2+, He2+, and Xe20+ at laboratory kinetic energies of 13 keV, 22.5 keV, and 300 keV, respectively. Intact singly charged C-60 monomers are the dominant reaction products in all three cases and this is accounted for by means of Monte Carlo calculations of energy transfer processes and a simple Arrhenius-type [C-60](n)(+) -> C-60(+) + (n - 1)C-60 evaporation model. Excitation energies in the range of only similar to 0.7 eV per C-60 molecule in a [C-60](13)(+) cluster are sufficient for complete evaporation and such low energies correspond to ion trajectories far outside the clusters. Still we observe singly and even doubly charged intact cluster ions which stem from even more distant collisions. For penetrating collisions the clusters become multiply charged and some of the individual molecules may be promptly fragmented in direct knock-out processes leading to efficient formations of new covalent systems. For Ar2+ and He2+ collisions, we observe very efficient C-119(+) and C-118(+) formation and molecular dynamics simulations suggest that they are covalent dumb-bell systems due to bonding between C-59(+) or C-58(+) and C-60 during cluster fragmentation. In the Ar2+ case, it is possible to form even smaller C-120-2m(+) molecules (m = 2-7), while no molecular fusion reactions are observed for the present Xe20+ collisions.

National Category
Atom and Molecular Physics and Optics
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-92922 (URN)10.1063/1.4812790 (DOI)000322203000028 ()
Funder
Swedish Research Council, 621-2008-3773Swedish Research Council, 621-2009-3468Swedish Research Council, 621-2011-4047EU, European Research Council, 246976
Note

AuthorCount:23;

Available from: 2013-08-30 Created: 2013-08-26 Last updated: 2017-12-06Bibliographically approved
3. Nonstatistical fragmentation of large molecules
Open this publication in new window or tab >>Nonstatistical fragmentation of large molecules
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2014 (English)In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 89, no 3, 032701Article in journal (Refereed) Published
Abstract [en]

We present experimental evidence for the dominance of prompt single-atom knockout in fragmenting collisions between large polycyclic aromatic hydrocarbon cations and He atoms at center-of-mass energies close to 100 eV. Such nonstatistical processes are shown to give highly reactive fragments. We argue that nonstatistical fragmentation is dominant for any sufficiently large molecular system under similar conditions.

National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-102212 (URN)10.1103/PhysRevA.89.032701 (DOI)000332340800004 ()
Funder
Swedish Research Council, 621-2012-3662, 621-2012-3660, 621-2011-4047
Note

AuthorCount: 18;

Available from: 2014-03-28 Created: 2014-03-28 Last updated: 2017-12-05Bibliographically approved
4. First storage of ion beams in the Double Electrostatic Ion-Ring Experiment: DESIREE
Open this publication in new window or tab >>First storage of ion beams in the Double Electrostatic Ion-Ring Experiment: DESIREE
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2013 (English)In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 84, no 5, 055115- p.Article in journal (Refereed) Published
Abstract [en]

We report on the first storage of ion beams in the Double ElectroStatic Ion Ring ExpEriment, DESIREE, at Stockholm University. We have produced beams of atomic carbon anions and small carbon anion molecules (C-n(-), n = 1, 2, 3, 4) in a sputter ion source. The ion beams were accelerated to 10 keV kinetic energy and stored in an electrostatic ion storage ring enclosed in a vacuum chamber at 13 K. For 10 keV C-2(-) molecular anions we measure the residual-gas limited beam storage lifetime to be 448 s +/- 18 s with two independent detector systems. Using the measured storage lifetimes we estimate that the residual gas pressure is in the 10(-14) mbar range. When high current ion beams are injected, the number of stored particles does not follow a single exponential decay law as would be expected for stored particles lost solely due to electron detachment in collision with the residual-gas. Instead, we observe a faster initial decay rate, which we ascribe to the effect of the space charge of the ion beam on the storage capacity.

National Category
Accelerator Physics and Instrumentation
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-92036 (URN)10.1063/1.4807702 (DOI)000319999300073 ()
Funder
Swedish Research Council, 2011-6314, 2011-4047, 2012-3662Knut and Alice Wallenberg Foundation
Note

AuthorCount:34;

Available from: 2013-07-16 Created: 2013-07-15 Last updated: 2017-12-06Bibliographically approved
5. Ions colliding with polycyclic aromatic hydrocarbon clusters
Open this publication in new window or tab >>Ions colliding with polycyclic aromatic hydrocarbon clusters
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2013 (English)In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T156, 014062- p.Article in journal (Refereed) Published
Abstract [en]

We have measured the ionization and fragmentation of polycyclic aromatic hydrocarbon (PAH) molecules and their clusters. We find that PAH clusters containing up to roughly 100 individual molecules fragment strongly following collisions with keV ions in low or high charge states (q). For both types of collisions, singly charged PAH molecules are found to be the dominant products but for very different reasons. A high-q ion projectile charge leads to strong multiple ionization of the PAH clusters and subsequent Coulomb explosions. A low-q ion projectile charge often leads to single ionization but stronger internal heating and long evaporation sequences with a singly charged PAH monomer as the end product. We have developed a Monte Carlo method for collision-induced heating of PAH clusters and present an evaporation model where the clusters cool slowly as most of the internal energies are stored in intramolecular vibrations and not in molecule-molecule vibrations.

National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-100403 (URN)10.1088/0031-8949/2013/T156/014062 (DOI)000329022300063 ()
Conference
16th International Conference on the Physics of Highly Charged Ions (HCI), SEP 02-07, 2012, Heidelberg, GERMANY
Note

AuthorCount:20;

Available from: 2014-02-03 Created: 2014-02-03 Last updated: 2017-12-06Bibliographically approved
6. Non-statistical fragmentation of PAHs and fullerenes in collisions with atoms
Open this publication in new window or tab >>Non-statistical fragmentation of PAHs and fullerenes in collisions with atoms
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2014 (English)In: International Journal of Mass Spectrometry, ISSN 1387-3806, E-ISSN 1873-2798, Vol. 365, 260-265 p.Article in journal (Refereed) Published
Abstract [en]

Non-statistical fragmentation processes may be important when Polycyclic Aromatic Hydrocarbon molecules (PAHs), fullerenes, or other large complex molecules collide with atoms and atomic ions. For collisions with hydrogen or helium this occurs for center-of-mass energies between a few tens to a few hundreds of electron volts and typically results in losses of single atoms. In such processes one forms much more reactive fragments than in statistical fragmentation, which instead are dominated by losses of C2- or C2H2-molecules (H-atoms) from fullerenes and PAHs, respectively. An enhanced reactivity has recently been demonstrated for van der Waals clusters of C60 molecules where prompt knockouts of single C-atoms from one of the fullerenes yield highly reactive C59+ fragments, which easily form covalent bonds with a C60 molecule inside the clusters

Keyword
Fullerene, PAH, Knockout, Ion collisions, Molecular fusion, Non-statistical fragmentation
National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-102211 (URN)10.1016/j.ijms.2013.12.013 (DOI)000338622200042 ()
Available from: 2014-03-28 Created: 2014-03-28 Last updated: 2017-12-05Bibliographically approved

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