Evidence for Jahn-Teller effects in endohedral fullerenes

Dunn, Janette L.; Rashed, Effat

Abstract

Endohedral fullerenes can be formed by encapsulating one or more atom or molecule inside the cavity of the fullerene molecule. When a light molecule is encapsulated, it will remain close to the centre of the fullerene molecule without any strong interactions with its environment. This allows the quantum-mechanical behaviour of the molecule to be probed almost as if it were a free molecule. However, energy levels deduced from inelastic neutron scattering (INS) and in infrared spectroscopy show some small splittings compared to the expected results for a free molecule. This indicates that the encapsulated molecule is not totally free from the effects of its environment. More specifically, the molecule must feel an environment that has a lower symmetry than that of an undistorted fullerene cage. We will review the evidence for symmetry-lowering in different types of endohedral fullerenes, and discuss whether the symmetry-lowering could be due to the Jahn-Teller (JT) effect. We will then present some results of a model for H2O@C60 which shows that the splittings seen in INS data could be explained in terms of JT distortions of the encapsulating fullerene cage. Nevertheless, the possibility that they could also be explained with a non-JT model can't be ruled out. 1. Introduction Atoms, ions or molecules can be inserted into the hollow core of a fullerene molecule to produce endohedral fullerenes. These are also called endofullerenes or, when it is a metal atom that is encapsulated, metallofullerenes. Efforts to synthesise endohedral fullerenes were first made soon after it was discovered that C 60 had a closed-cage structure [1, 2]. In fact, doping with La ions played an important role in supporting the hypothesis that C 60 does indeed have a closed-cage structure [3, 4]. Many reviews of endohedral fullerenes have been published, including a general review [5] and reviews of metallofullerenes [6, 7, 8], aspects related to interstallar endohedral fullerenes [9] and the effects of polarisability [10]. Endohedral fullerenes containing rare gas atoms (He, Ne, Ar) or some alkali metals can be formed in small quantities by bombarding empty fullerenes with ions having energies from ≈ 6 eV to ≈ 50 eV [11, 12] or treating fullerene powder under forced conditions [13]. Other endohedral fullerenes containing one or two atoms of rare gas, transition metal or alkali metal atoms can be formed using standard processes for the formation of fullerenes, such as laser graphite ablation or arc discharge [14, 6, 7, 15, 16]. Lists of the earliest-known endohedral fullerenes containing one or two encapsulated atoms, along with their methods of preparation, can be found in Ref. [17]. Fullerenes can also encapsulate larger clusters. For example, encapsulation of metallic clusters can stabilise giant fullerenes (C 90 to C 104) [18], and a novel planar quinary cluster can

Citation

Dunn, J. L., & Rashed, E. (2018). Evidence for Jahn-Teller effects in endohedral fullerenes. Journal of Physics: Conference Series, 1148(1), https://doi.org/10.1088/1742-6596/1148/1/012003

• Journal Article Type: Article
• Acceptance Date: Oct 23, 2018
• Online Publication Date: Dec 22, 2018
• Publication Date: Dec 22, 2018
• Deposit Date: Nov 20, 2018
• Publicly Available Date: Nov 21, 2018
• Journal: Journal of Physics: Conference Series
• Print ISSN: 1742-6588
• Electronic ISSN: 1742-6596
• Publisher: IOP Publishing
• Peer Reviewed: Peer Reviewed
• Volume: 1148
• Issue: 1
• DOI: https://doi.org/10.1088/1742-6596/1148/1/012003
• Public URL: https://nottingham-repository.worktribe.com/output/1291652
• Publisher URL: http://iopscience.iop.org/article/10.1088/1742-6596/1148/1/012003
• Contract Date: Nov 20, 2018