Buckminster fullerene
Inhaltsverzeichnis
Giant breathing mode
As the fingerprint of the response (relaxation) of the Buckminster fullerene C60, electronically excited by an intense laser field, the breathing mode with very large amplitude is excited due to electron-vibration coupling [1].
Excitation of giant breathing mode
Dynamics of C60 excited by a 30 fs laser with ω = 3 eV and an intensity of 3.3e13 W/cm^2.
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In a pump-probe experiment, this effect can be observed [1], because the energy absorbed from the probe pulse and, thus, the multiplicity of the measured fragments depend strongly on the actual cage radius R(t) and thus on the delay time.
Typical pump-probe scenario
Dynamics of C60 excited by a pump and a delayed probe pulse.
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The pump pulse induces breathing, the probe pulse leads to multifragmentation. The number of fragments oscillates as a function of the delay time as the radius oscillates.
Symmetric fission
The amount of energy deposited into C60 by a short laser field strongly depends on the molecular orientation with respect to the laser polarization direction [2]. In consequence, subsequent electron-vibration coupling leads to different nuclear relaxation mechanisms with mainly three pathways: excitation of the breathing mode, formation of deformed cagelike complexes ("isomers"), and fragmentation predominantly into two large pieces ("symmetric fission").
Dynamics of C60 excited by a 30 fs laser with λ = 800 nm and an intensity of 6e14 W/cm^2 (vertical laser polarization direction).
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For molecular orientations with highest energy absorption the cluster fragments basically into two, nearly equally sized large pieces. The strongly deformed caplike fission fragments are highly unstable and are expected to decay into smaller fragments on a picosecond time scale. The mechanism of this symmetric fission explains nicely the experimental observation of the abrupt occurrence of large fragments in the mass spectra of fs-pulses above a certain threshold intensity.
- T. Laarmann, I. Shchatsinin, A. Stalmashonak, M. Boyle, N. Zhavoronkov, J. Handt, R. Schmidt, C.P. Schulz, and I.V. Hertel, Control of Giant Breathing Motion in C60 with Temporally Shaped Laser Pulses, Phys. Rev. Lett. 98, 058302 (2007).
- M. Fischer, J. Handt, G. Seifert, and R. Schmidt,
Orientation dependence of energy absorption and relaxation dynamics of C60 in fs-laser pulses, Phys. Rev. A 88, 061403(R) (2013).