Book of Abstracts Book of Abstracts - Universität Konstanz

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68
Femtosecond Laser-Induced Fusion of Fullerenes Inside Clusters
Martin Hedén, Klavs Hansen, Eleanor E. B. Campbell
Department of Physics, Göteborg University, SE-41296 Göteborg, Sweden
The interaction of fullerene molecules with femtosecond laser radiation has been the subject
of much interest in recent years. One interesting observation is the clear separation of different
ionisation mechanisms that can be observed as a function of the timescale for the excitation [1].
We have shown that for intermediate timescales (ca. 70-300 fs) the ionisation can be largely
regarded as a thermal electron emission from the equilibrated hot electron system before energy
is transferred to the nuclear degrees of freedom [2]. Interesting dynamics have also been
observed in collisions between fullerenes leading to molecular fusion of the collision partners
and the formation of a metastable larger fullerene that subsequently decays by the emission of
C2 molecules [3].
In this contribution we combine these two topics of recent research interest and show that it is
possible to induce molecular fusion of fullerenes that are weakly (van der Waals) bonded in
molecular clusters. Fig. 1. Shows a typical mass spectrum of the clusters after laser irradiation.
The fragmentation pattern is clearly reminiscent of C2 emission from a large fullerene-like
structure. We show that this observation is consistent with our knowledge of both the ionisation
mechanisms of C60 on irradiation with fs laser pulses and with our knowledge of the energetic
threshold for fullerene fusion and the C2 decay of large fullerenes. It is shown that substantial
atomic rearrangement can take place on a timescale shorter than that needed for the complete
destruction of the highly excited cluster. This is different for the observations made in
experiments where fullerene clusters are collided with highly charged ions [4]. Reasons for the
difference will be discussed.
N
Figure 1. Time-of-flight mass spectrum from fullerene clusters after excitation with a 200 fs laser pulse.A distribution
of fragment masses is seen corresponding to each cluster size, with a mass separation of the fragments in each
distribution of C2. This is a clear indication that the clusters have ionised and then had time for extensive atomic
rearrangement to form a single large fullerene-like structure before the original clusters completely disintegrate.
References
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[1] E.E.B. Campbell, K. Hansen, K. Hoffmann, G. Korn, M. Tchaplyguine, M. Wittmann, I.V. Hertel,
Phys. Rev. Lett., 84 2128 (2000)
[2] K. Hansen, K. Hoffmann, E.E.B. Campbell, J. Chem. Phys. 119 2513 (2003).
[3] E.E.B. Campbell, A.V. Glotov, A. Lassesson, R.D. Levine, C.R. Physique 3 (2002) 341
[4] B. Manil, L. Maunoury, B. A. Huber, J. Jensen, H. T. Schmidt, H. Zettergren, H. Cederquist, S.
Tomita and P. Hvelplund, Phys. Rev. Lett. 21 (2003) 215504