| 1. |
- 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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| 2. |
- Bulgakov, Alexander, 1956, et al.
(author)
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Phosphorus cluster production by laser ablation
- 2004
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In: Applied Physics A. - : Springer Science and Business Media LLC. - 0947-8396 .- 1432-0630. ; 79, s. 1369-1372
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Journal article (peer-reviewed)abstract
- Neutral and charged phosphorus clusters of a wide size range have been produced by pulsed laser ablation (PLA) in vacuum at 532, 337, and 193 nm ablating wavelengths and investigated by time-of-flight mass spectrometry. The neutral Pn clusters are even-numbered with local abundance maxima at n=10 and 14, while the cationic and anionic clusters are preferentially odd-numbered with P7+, P21+, and P17- being the most abundant ions. The dominance of the magic clusters is more pronounced at 337-nm ablation that is explained by efficient direct ejection of their building blocks under these conditions. Nanocrystalline phosphorus films have been produced by PLA in ambient helium gas.
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| 3. |
- Lassesson, Andreas, 1976, et al.
(author)
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A femtosecond laser study of the endoral fullerenes Li@C60 and La@C82
- 2005
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In: Eur. Phys. J. D. - : Springer Science and Business Media LLC. - 1434-6060. ; 34, s. 205-209
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Journal article (peer-reviewed)abstract
- The endohedral fullerenes La@C82 and Li@C60 have been studied in the gas phase with femtosecond laser excitation. The two molecules show qualitatively the same behaviour with respect to ion yield vs. pulse energy, but markedly different fragmentation patterns, with La@C82 fragmenting via the shrink-wrap mechanism and Li@C60 predominantly losing the metal atom in the first fragmentation step. The ion yields and electron energy distributions of La@C82 agree well with a recently developed model for fs laser ionisation of C60.
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| 4. |
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| 5. |
- Lassesson, Andreas, 1976, et al.
(author)
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Formation of small lanthanum-carbide ions from laser induced fragmentation of La@C-82
- 2003
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In: Journal of Chemical Physics. - : AIP Publishing. - 1089-7690 .- 0021-9606. ; 119:11, s. 5591-5600
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Journal article (peer-reviewed)abstract
- The fragmentation behavior of the endohedral metallofullerene La@C-82 was studied using gas phase time-of-flight mass spectrometry. The results were compared with the fragmentation of C-60. When the metallofullerene was excited by a 337 nm ns laser, small lanthanum-carbide fragments LaCn+, n=0-6, were detected. A simple statistical maximum entropy model was used to simulate the excitation energy dependence of the loss of the LaCn+ molecules as well as C-2 evaporation to form smaller metallofullerenes. By comparing experimental ion intensities with the model, the appearance energies of LaCn+, n=0-6, were found to lie above 65 eV. The lanthanum-carbide fragments ejected from La@C-82 decrease in size with increasing internal energy. The ejection of La+ and LaC2+ is preferred at the expense of larger fragments such as LaC4+ and metallofullerenes at the higher excitation. (C) 2003 American Institute of Physics.
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| 6. |
- Lassesson, Andreas, 1976, et al.
(author)
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Investigations into the fragmentation and ionization of highly excited La@C-82
- 2002
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In: Journal of Chemical Physics. - : AIP Publishing. - 1089-7690 .- 0021-9606. ; 117:21, s. 9811-9817
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Journal article (peer-reviewed)abstract
- We report the first measurements of delayed ionization of the metallofullerene La@C-82. When highly excited in laser desorption, La@C-82 was found to ionize over several microseconds. The rate of delayed ionization of La@C-82 was compared to C-60 under the same extraction conditions, and found to be significantly different. A theoretical model was used for the fitting of the ion signal of the two fullerenes. The metallofullerene results can be fitted well over a time window
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| 7. |
- Popok, Vladimir, 1966, et al.
(author)
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Conductance and EPR study of the endohedral fullerene Li@C60
- 2005
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In: Solid State Communications. ; 133:8, s. 499-503
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Journal article (peer-reviewed)abstract
- Thin films and bulk samples of endohedral fullerenes Li@C60 are studied using current-voltage (I-V) measurements and electron paramagnetic resonance (EPR). Electrical measurements show a linear behaviour for the I-V curves and give an average resistivity of ca. 1.5 kOhmcm for thin Li@C60 films deposited in vacuum, four orders of magnitude lower than C60 samples. A drastic effect on the conductance, lowering it to the values typical for C60, is observed when the Li@C60 samples are exposed to ambient atmosphere. No additional paramagnetic centres (PCs) are found for the Li@C60 compared to C60 that can be related to the formation of dimers or trimers of the endohedral fullerene molecules. However, the presence of the Li atoms in the fullerene cages contributes to a change of the spin-spin and spin-lattice relaxation times. The spin-lattice relaxation time becomes 4 orders of magnitude longer compared to the spin-spin relaxation time.
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| 8. |
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