Fullerene fusion induced by highly charged ion impact on clusters of fullerenes

H. Zettergren*,1, P. Hvelplund*, H. T. Schmidt†, H. Cederquist†, J. Jensen‡, S. Tomita#, B. Manil&, L.
Maunory, and B. A. Huber&

* Department of Physics and Astronomy, University of Aarhus, DK-8000 Aarhus C, Denmark
† Department of Physics, Stockholm University, AlbaNova University Center, S-10691 Stockholm, Sweden
‡ Department of Physics, Chemistry and Biology (IFM), Linkцping University, SE-581 83 Linkцping, Sweden
# Institute of Applied Physics, University of Tsukuba, Tsukuba, Ibaraki 305-0006, Japan
&Centre de Recherche sur les Ions, les Matйriaux et la Photonique (CIMAP), Boulevard Henry Becquerel,
F-14070 Caen Cedex 05, France

Synopsis

We have observed fullerene fusion induced by highly charged Xe20+ impact on weakly bound clusters of fullerenes. A characteristic distribution of singly charged fused even n Cn fullerenes with 60

Fusions of fullerene monomer cages have been observed in laser vaporization from a substrate [1], in collision experiments between fullerenes [2], and when weakly bound clusters of fullerenes, [C60]n, are excited by femtosecond laser pulses [3]. Cage fusion of two fullerene monomers (C60) to form C120 is associated with a high energy barrier of about 80-85 eV [4], and thus the monomer need to have at least this amount of internal excitation energy to be fused. In contrast, slow highly charged ions are known to be efficient ionization agents in fullerene collision experiments, where only small amounts of energy are transferred to the target in distant collisions whereas frontal collisions leads to multi-fragmentation of the fullerene cages. In this respect, we report the somewhat surprising observation of fullerene fusion induced by highly charged ion impact on van der Waals clusters of fullerenes.

In the present experiment, neutral clusters of fullerenes are produced in a cluster aggregation source, giving a temperature dependent distribution of van der Waals clusters of fullerenes. These clusters then interact with a pulsed Xe20+-beam, and the so formed ions (intact weakly bound clusters of fullerenes, fragments, and cage-fused fullerenes) are analyzed by means of a linear time-of-flight spectrometer. For low volume densities of fullerene monomers (i.e. for low fullerene oven temperatures), a distribution of small cluster sizes are observed in the mass spectra, whereas increased temperatures leads to a broader distribution extending to larger cluster sizes. In addition, a clear signature of fullerene-cage fusion is observed for high oven temperatures (see Fig. 1). This is manifested as a distribution of singly charged even n Cn fullerenes in the 60

References

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