Helium-fullerene complex

Arc discharge [25] is initially used for producing C60 fullerenes. Nanotubes are produced by arc vaporization of two carbon rods placed in a chamber that is filled with low pressure inert gas (helium, argon). The composition of the graphite anode determines the type of CNTs produced. A pure graphite anode produce preferably MWNT while catalyst (Fe, Co, Ni, Y or Mo) doped graphite anode produces mainly SWNT. This technique normally produces a complex mixture of components, and requires further purification to separate the CNTs from the soot and the residual catalytic metals present in the crude product. 

C. G. Joslin, C. G. Gray, and S. Goldman, Chem. Phys. Lett., 227, 405 (1994). Infrared Rotation and Vibration-Rotation Bands of Endohedral Fullerene Complexes. Helium in C60-Derived Nanotubes. 

The so-called cryptophanes which are structurally related to 10 have shown to be capable of complexing stable molecules like methane or various fluorocarbons [9] and the number of fullerenes with a content - helium, neon, numerous metal ions [10,11] is rapidly increasing. 

It might be mentioned that there is quite a large empty space in the interior of the fullerene molecule. It has proven possible to trap various rare-gas atoms and small molecules within the fullerene interior, and the subject has been studied in some detail. Helium and argon, for example, can be inserted into the fullerene cage at high temperatures and pressures. The resulting structures are referred to as endohedral complexes, and they can be identified by mass spectrometry. ... 

It may be of interest that the helium-fullerene complex is in fact a natural product. It has been detected in distant stars, where it has existed in large tonnage amounts for millions of years. This recalls to mind the fact that helium was discovered in the sun (by the presence of intense lines in the visible spectrum). This fact was indicated by the name chosen for it, which is from the Greek word helios, meaning sun. It was only later discovered to exist in Earth s crust. 

Fullerenes are hollow can cage atoms as large as xenon. The endohedral nature of a complex may be demonstrated by its stability. (HeCgg) , formed by collisions of C, with helium gas, survives... 

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