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Ions colliding with clusters of fullerenes-Decay pathways and covalent bond formations
Stockholm University, Faculty of Science, Department of Physics.
Stockholm University, Faculty of Science, Department of Physics.
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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.

Place, publisher, year, edition, pages
2013. Vol. 139, no 3, 034309
National Category
Atom and Molecular Physics and Optics
Research subject
Physics
Identifiers
URN: urn:nbn:se:su:diva-92922DOI: 10.1063/1.4812790ISI: 000322203000028OAI: oai:DiVA.org:su-92922DiVA: diva2:644334
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
In thesis
1. Ions colliding with Polycyclic Aromatic Hydrocarbons and Fullerenes
Open this publication in new window or tab >>Ions colliding with Polycyclic Aromatic Hydrocarbons and Fullerenes
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis a series of experiments on collisions between atomic projectile ions at keV energies and target vapors of either isolated molecules or van der Waals clusters is presented and analyzed. The atomic ions are produced in an Electron Cyclotron Resonance (ECR) ion source, accelerated and guided into the target volume. The charged target collision products are mass-to-charge analyzed in a time-of-flight spectrometer. The Polycyclic Aromatic Hyrdrocarbons (PAHs) Anthracene (C14H10), Coronene (C24H12), two C16H10 isomers, Pyrene and Fluoranthene, and the fullerene C60 are examined.

For projectile ions in low charge states, small impact parameter collisions dominate, which leads to internal heating of the target. With isolated molecules as targets, this typically results in ionization and often also in fragmentation. For cluster targets energy and charge are rapidly distributed among the cluster building blocks. This is followed by cluster evaporation and very limited fragmentation of the individual molecules. C119+ and C118+ are observed as products. These are due to the formation of the reactive C58/59+ ions by direct knockout processes, which react with another C60 of the cluster to form dumb-bell shaped molecules.

For projectile ions of high charge (Xe20+) larger impact parameters dominate, leading to little internal heating. For isolated molecule targets, intact molecular ions are the main collision products. Charged fragments stem mostly from multifragmentation following ionization to high charge states. For cluster targets, the collision products consist mainly of singly charged monomers. Fragmentation of the individual molecules is comparatively strong. This suggests a quick distribution of charges followed by a Coulomb explosion, which leads to internal heating.

The results show that weakly bound clusters do not sustain the impact of keV-ions and that it is possible to form new molecular structures.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University, 2013. 118 p.
National Category
Atom and Molecular Physics and Optics
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-88427 (URN)978-91-7447-649-1 (ISBN)
Public defence
2013-04-30, lecture hall FD5, AlbaNova universitetscentrum, Roslagstullbacken 21, Stockholm, 10:15 (English)
Opponent
Supervisors
Note

At the time of doctoral defense, the following papers were unpublished and had a status as follows: Paper 5: Submitted. Paper 6: Submitted.

Available from: 2013-04-08 Created: 2013-03-14 Last updated: 2014-03-28Bibliographically approved
2. Statistical and Non-statistical frag-mentation of large molecules in col-lisions with atoms: Polycyclic Aromatic Hydrocarbons and Fullerenes
Open this publication in new window or tab >>Statistical and Non-statistical frag-mentation of large molecules in col-lisions with atoms: Polycyclic Aromatic Hydrocarbons and Fullerenes
2014 (English)Licentiate thesis, comprehensive summary (Other academic)
Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University, 2014. 46 p.
National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-102005 (URN)978-91-7447-869-3 (ISBN)
Presentation
2014-04-11, FB53, Albanova universitetscentrum, Roslagstullsbacken 21, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

At the time of the seminar the following papers were unpublished and had a status as follows:  Paper 3: Epubl ahead of print; Paper 5: Manuscript.

Available from: 2014-03-28 Created: 2014-03-20 Last updated: 2014-03-28Bibliographically approved
3. Collision Induced Fragmentation of Molecules and Molecular Clusters: Knockout Driven Reactions in Fullerenes and PAHs
Open this publication in new window or tab >>Collision Induced Fragmentation of Molecules and Molecular Clusters: Knockout Driven Reactions in Fullerenes and PAHs
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:nbn:se:su:diva-103501 (URN)
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
4. Ions colliding with molecules and molecular clusters: fragmentation and growth processes
Open this publication in new window or tab >>Ions colliding with molecules and molecular clusters: fragmentation and growth processes
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this work we will discuss fragmentation and molecular growth processes in collisions of Polycyclic Aromatic Hydrocarbon (PAH) molecules, fullerenes, or their clusters with atoms or atomic ions. Simple collision models as well as molecular structure calculations are used to aid the interpretations of the present and other experimental results. Fragmentation features at center-of-mass collision energies around 10 keV are dominated by interactions between the fast ion/atom and the electron cloud in the molecules/clusters (electronic stopping processes). This electronic excitation energy is rapidly distributed on the vibrational degrees of freedom of the molecule or of the molecules in a cluster and may result in fragmentation. Here, the fragmentation is statistical and favors the lowest-energy dissociation channels which are losses of intact molecules from clusters, H- and C2H2-losses from isolated PAHs, and C2-loss from fullerene monomers. We will also discuss the possibility of formation of molecular H2 direct from native PAHs which reach high enough energies when interacting with ions, electrons, or photons.

For the experiments at lower center of mass collision energies (~100 eV) a single atom may be knocked out in close atom-atom interaction. Such non-statistical fragmentation are due to nuclear stopping processes and gives highly reactive fragments which may form covalent bonds with other molecules in a cluster on very short time scales (picoseconds). This process may be important when considering the formation of new species. For collision between 12 keV Ar2+ and clusters of pyrene (C16H10) molecules, new molecules, e.g. C17H10+, C30H18+, C31H19+, etc are detected. We also observe molecular fusion processes for He and Ar ions colliding with clusters of C60 molecules. These and related molecular fusion processes may play a key role for understanding molecular growth processes under certain astrophysical conditions.

Place, publisher, year, edition, pages
Stockholm University, 2015. 38 p.
Keyword
PAH, H2, C60, fragmentation
National Category
Atom and Molecular Physics and Optics
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-117114 (URN)978-91-7649-063-1 (ISBN)
Public defence
2015-06-11, FD5, AlbaNova Universitetscentrum, Roslagstullsbacken 21, Stockholm, 13:00 (English)
Opponent
Supervisors
Available from: 2015-05-20 Created: 2015-05-07 Last updated: 2015-05-22Bibliographically approved
5. Molecular Hole Punching: Impulse Driven Reactions in Molecules and Molecular Clusters
Open this publication in new window or tab >>Molecular Hole Punching: Impulse Driven Reactions in Molecules and Molecular Clusters
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

When molecules are excited by photons or energetic particles, they will cool through the emission of photons, electrons, or by fragmenting. Such processes are often thermal as they occur after the excitation energy has been redistributed across all degrees-of-freedom in the system. Collisions with atoms or ions may also lead to ultrafast fragmentation in Rutherford-like scattering processes, where one or several atoms can literally be knocked out of the molecule by the incoming projectile before the energy can be completely redistributed. The resulting fragmentation pathways can in such knockout processes be very different from those in thermal processes.

This thesis covers extensive studies of collisions between ions/atoms and isolated Polycyclic Aromatic Hydrocarbon (PAH) molecules, isolated fullerene molecules, or clusters of these. The high stabilities and distinct fragmentation channels make these types of molecules excellent test cases for characterizing knockout-driven fragmentation and the reactions that these processes can lead to. I will present experimental measurements for a wide range of energies and compare them with my own molecular dynamics simulations and quantum chemical calculations. In this thesis, I present an in-depth study of the role of knockout in the energetic processing of molecules and clusters. The competition between knockout and thermally driven fragmentation is discussed in detail.

Knockout-driven fragmentation is shown to result in exotic fragments that are far more reactive than the intact parent molecules or fragments from thermal processes. When such reactive species are formed within molecular clusters efficient molecular growth can take place on sub-picosecond timescales. The cluster environments are crucial here because they protect the newly formed molecules by absorbing excess energy. This is a possible pathway for the growth of large PAHs, fullerenes, and similar carbonaceous complexes found in, for instance, the interstellar medium.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University, 2016. 74 p.
Keyword
PAHs, Fullernes, Reactions, Clusters, Interstellar Medium, Fragmentation, Non-Statistical Fragmentation, Collisions, Experiments, Molecular Dynamics, Density Functional Theory
National Category
Atom and Molecular Physics and Optics
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-129523 (URN)978-91-7649-436-3 (ISBN)
Public defence
2016-06-10, 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 1: Submitted.

Available from: 2016-05-18 Created: 2016-04-25 Last updated: 2017-02-17Bibliographically approved

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