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| 2. |
- Campbell, Eleanor E B, 1960, et al.
(författare)
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Ionisation of Fullerenes and Fullerene Clusters using Ultrashort Laser Pulses
- 2006
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Ingår i: Photochem. Photobiol. Sci.. - : Springer Science and Business Media LLC. - 1474-905X. ; 5, s. 1183-1189
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Tidskriftsartikel (refereegranskat)abstract
- We give a brief review of the literature concerning the ultra-short pulse ionisation of fullerenes in the gas phase. Emphasis is placed on the excitation time dependence of different ionisation regimes as manifested by photoelectron spectroscopy. The ionisation rates are modelled for the intermediate situation where the excitation energy is equilibrated between electronic degrees of freedom but not yet coupled to vibrational degrees of freedom. The model is shown to describe many aspects of the experiments. New results are presented on the intra-cluster molecular fusion of fullerene molecules when van der Waals bound clusters of fullerenes are exposed to ultra-short laser pulses. Pump–probe measurements give a decay time constant for the intra-cluster fusion reaction of 520 ± 55 fs. A comparison with monomer ionisation results suggests that the time window for the fusion reaction is influenced by the coupling of the electronic excitation energy to vibrational degrees of freedom of the molecules in the cluster.
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| 3. |
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| 4. |
- Hansen, Klavs, 1958, et al.
(författare)
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Competition between fusion and intra-cluster fusion in highly excited fullerene clusters
- 2007
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Ingår i: Israel Journal of Chemistry. - 0021-2148. ; 47
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Tidskriftsartikel (refereegranskat)abstract
- The occurrence of intra-cluster fusion of fullerene molecules inside van der Waals bound fullerene clusters can be observed following femtosecond laser excitation. We show that the fusion reaction competes with the fission of multiply charged clusters. Energetic barriers to the reaction of at least 85 eV have to be overcome, similar to the energetic barriers to molecular fusion observed in fullerene ion–neutral fullerene collision experiments.
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| 5. |
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| 6. |
- Johansson, J. O., et al.
(författare)
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Anisotropic hot electron emission from fullerenes
- 2012
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 136:16
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Tidskriftsartikel (refereegranskat)abstract
- Photoelectron spectra for fullerenes C-60 and C-70 ionized using 800 nm laser pulses with pulse durations from 120 to 1000 fs show thermal electron kinetic energy distributions but they also exhibit angular anisotropy with respect to the laser light polarization. The effective temperature of electrons, measured along the laser polarization direction, is significantly higher than in the perpendicular direction. We explain this observation by considering that the emission of the thermal electrons is uncorrelated with the phase of the laser pulse, unlike directly ionized electrons, and, depending on the time of emission, they may experience an additional "kick" from the vector potential of the laser field when they are emitted from the molecule. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4704828]
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| 7. |
- Kjellberg, Mikael, 1980, et al.
(författare)
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Femtosecond electron spectroscopy of coronene, benzo[GHI]perylene and anthracene
- 2010
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Ingår i: Journal of Chemical Physics. - 0021-9606. ; 133:7
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Tidskriftsartikel (refereegranskat)abstract
- The large polycyclic aromatic hydrocarbon molecules coronene, benzo[GHI]perylene, and anthracene have been ionized with femtosecond laser pulses at low laser intensities and the ionization process studied with velocity map imaging spectroscopy, supplemented with ion yield measurements. The electron spectra of coronene and benzo[GHI]perylene are structureless. Based on fluence and pulse duration dependence measurements, it is shown that the electron spectra are not produced in field ionization processes, and the ionization mechanism is identified to be a quasithermal statistical electron emission, previously suggested for the fullerenes C60 and C70. The anthracene photoelectron spectra are dominated by above threshold ionization features, but with some indication of quasithermal ionization at longer pulses.
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| 8. |
- Kjellberg, Mikael, 1980
(författare)
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Ionization of large molecules with short laser pulses
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The decay dynamics of fullerenes and polyaromatic hydrocarbons (PAH) after femtosecond-laser excitation have been studied experimentally by electron momentum mapping and mass spectrometry. The electron spectra of fullerenes and large PAH-molecules were found to be exponentially decreasing with energy without any distinct peaks outside the photon energy. This is interpreted as a statistical electron emission from a transient hot, highly excited, electron system where vibrations are still cold. The smooth electron distributions observed were shown not to be due to tunneling ionization. The photoelectron distributions showed a prolongation along the laser eld polarization axis, which was interpreted as eld-assisted thermal ionization. For the smallest molecule in the study, anthracene, a transition to atomic like, above threshold ionization, was observed. Molecular fusion of clusters of fullerenes, formed at liquid nitrogen temperature, after fs-laser excitation has also been studied. Products of up to ve fused molecules were observed. The mass spectra are the results of several processes including multiple ionization, evaporation of intact fullerenes and post-fusion C2 evaporation.
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| 9. |
- Kjellberg, Mikael, 1980, et al.
(författare)
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Momentum map imaging photoelectron spectroscopy of fullerenes with femtosecond laser pulses
- 2010
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Ingår i: Physical Review A. - 1050-2947. ; 81:2
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Tidskriftsartikel (refereegranskat)abstract
- Photoelectron spectra of C60 and C70, ionized with ultrashort laser pulses, are measured with a momentum-map-imaging electron spectrometer. Above the photon energy, 1.6 eV, the spectra are essentially structureless and well described by Boltzmann distributions, with temperatures on the order of 104 K. This result is similar to previous results for C60 using a time-of-flight electron spectrometer, which are confirmed in this study. Comparisons of electron energy distributions recorded for identical laser intensities but for different pulse durations demonstrate unambiguously that a significant fraction of the electrons are emitted in quasithermal processes and results argue strongly against a field ionization or direct multiphoton ionization mechanism. For electron energies above the photon energy, which account for about half the intensity, the whole signal is consistent with this quasithermal emission.
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| 10. |
- Prasalovich, Sergei, 1976, et al.
(författare)
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Surface entropy of rare-gas clusters
- 2005
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Ingår i: J. Chem. Phys.. - : AIP Publishing. - 0021-9606. ; 123
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Tidskriftsartikel (refereegranskat)abstract
- Abundances of Ar and Xe clusters produced in a supersonic expansion source are inverted to find relative dissociation energies. The values around the shell and subshell closings at N=55, 71, and 147 differ from theoretical values derived from ground-state energies of Lennard-Jones clusters. A significant part of the difference can be accounted for by the conformational entropies of surface atoms and vacancies.
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