| 1. |
- Hedén, Martin, 1976, et al.
(author)
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Thermal radiation from CN+ and La@CN
- 2005
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In: J. Chem. Phys.. - : AIP Publishing. - 0021-9606. ; 123
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Journal article (peer-reviewed)abstract
- The radiative cooling of positively charged fullerene and endohedral fullerene fragments of C60, C70, C84, and La@C82 has been measured in a time-of-flight mass spectrometer. The radiative cooling is measured via its influence on the metastable decay. The emissivity extracted from the data is between 4×10–4 and 13×10–4. These values agree fairly well with the emissivity calculated from considering the low-energy tail of the surface plasmon. No major difference is found in the emission behavior of empty and endohedral fullerenes.
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| 2. |
- Mehlig, Kirsten, 1964, et al.
(author)
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Energy distributions in multiple photon absorption experiments
- 2004
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In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 120, s. 4281-4288
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Journal article (peer-reviewed)abstract
- Photofragmentation experiments on molecules and clusters often involve multiple photon absorption. The distributions of the absorbed number of photons are frequently approximated by Poisson distributions. For realistic laser beam profiles, this approximation fails seriously due to the spatial variation of the mean number of absorbed photons across the laser beam. We calculate the distribution of absorbed energy for various laser and molecular-beam parameters. For a Gaussian laser beam, the spatially averaged distributions have a power-law behavior for low energy with a cutoff at an energy which is proportional to fluence. The power varies between –1 for an almost parallel laser beam and –5/2 for a divergent beam (on the scale of the molecular beam). We show that the experimental abundance spectra of fullerenes and small carbon clusters can be used to reconstruct the distribution of internal energy in the excited C60 molecule prior to fragmentation and find good agreement with the calculated curves
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| 3. |
- Boyle, Mark, et al.
(author)
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Excitation dynamics of Rydberg states in C60
- 2005
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In: European Physical Journal D. - : Springer Science and Business Media LLC. - 1434-6060 .- 1434-6079. ; 36, s. 339-351
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Journal article (peer-reviewed)abstract
- The electron and nuclear dynamics of C60 fullerenes irradiated with femtosecond laser pulses are investigated with photoelectron and photoion spectroscopy. The focus of this work is the detailed exploration of the population mechanism of Rydberg levels within the excitation process of neutral C60. The effect of excitation wavelength, intensity, chirp, and polarization on the kinetic energy distribution of photoelectrons in single-pulse experiments gives first insight into the underlying processes. In combination with time-resolved two-color pump-probe spectroscopy depending on either pump, or probe pulse intensity, a more complete picture of the interaction can be drawn. The results point towards a very interesting but nevertheless complex behavior including four steps: (i) non-adiabatic multielectron excitation of the HOMO (hu) → LUMO+1 (t1g) transition; (ii) thermalization within the hot electron cloud on a time scale below 100fs, followed by a coupling of energy to vibrational modes of the molecule via doorway state(s); (iii) population of electronically excited Rydberg states by multiphoton absorption, and (iv) single photon ionization from the excited Rydberg states. This excitation process results in a characteristic sequence of photoelectron lines in the photoemission spectra. The comparison of the experimental results with recent theoretical work gives convincing evidence that non-adiabatic multielectron dynamics (NMED) plays a key role for the understanding of the response of C60 to short-pulse laser radiation.
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| 4. |
- Boyle, Mark, et al.
(author)
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Two colour pump-probe study and internal energy dependence of Rydberg state excitation
- 2004
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In: Physical Review A. - 1050-2947. ; 70
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Journal article (peer-reviewed)abstract
- Excitation of Rydberg states in isolated C60 is studied by time-resolved photoelectron spectroscopy in a femtosecond two-color pump-probe experiment. The relaxation time for electron-electron interaction is determined to be approximately 100 fs with the t1g(LUMO + 1) orbital being considered to define the doorway state in a nonadiabatic multielectron excitation process. The internal energy stored in vibrational modes of the C60 at 770 K is found to support the excitation process very efficiently while in "cold" C60 (80 K), no significant Rydberg population is detected.
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| 5. |
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| 6. |
- Campbell, Eleanor E B, 1960, et al.
(author)
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Ionisation of Fullerenes and Fullerene Clusters using Ultrashort Laser Pulses
- 2006
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In: Photochem. Photobiol. Sci.. - : Springer Science and Business Media LLC. - 1474-905X. ; 5, s. 1183-1189
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Journal article (peer-reviewed)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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| 7. |
- Hedén, Martin, 1976, et al.
(author)
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Determination of the triplet state lifetime of vibrationally excited C-60
- 2003
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In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 118:16, s. 7161-7164
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Journal article (peer-reviewed)abstract
- The lifetime of the ground triplet state of vibrationally excited C-60 has been determined in a two-color pump-probe experiment. An intense pump pulse (337 nm, 4 ns) was used to excite the neutral molecules. The triplet state was probed via single photon ionization with a weak probe pulse (193 nm). The lifetime was found to be on the order of 1 mus. This is rather low to explain recent delayed ionization results but higher than expected from an extrapolation of earlier measurements at lower temperatures. (C) 2003 American Institute of Physics.
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| 8. |
- Hedén, Martin, 1976, et al.
(author)
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Molecular Fusion of (C60)N Clusters in the Gas Phase after Femtosecond Laser Irradiation
- 2005
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In: Phys. Rev. A. - 1050-2947. ; 71
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Journal article (peer-reviewed)abstract
- We report observation of molecular fusion of (C60)N+ clusters to form large fullerene molecules after excitation by 800-nm femtosecond laser pulses. The fused species decay by undergoing C2 fragmentation. Such fragmentation behavior for excited clusters of fullerene molecules can be understood in terms of the energetics of molecular fusion as determined previously from fullerene-fullerene collision experiments. Within a certain excitation energy window, there is sufficient time for a substantial atomic rearrangement to take place within the clusters before they dissociate. Below this energy window there is not sufficient internal energy for molecular fusion to occur while above the energy window multiple ionization followed by breakup of the clusters dominates.
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| 10. |
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