Noble gases can also make endohedral fullerene compounds when the noble gas atom is pushed inside a fullerene molecule. In 1993, it was discovered that when C60 is put under pressure of about 3 bar of Helium or Neon, He@C60 and Ne@C60 are made. Only about one out of every 650,000 C60 were found with a helium atom. But with more pressures (about 3000 bar), it is possible to get as much as 0.1%. Endohedral molecules with argon, krypton and xenon have also been made, as well as other compounds of He@C60.
↑Martin Saunders, Hugo A. Jimenez-Vazquez, R. James Cross, Stanley Mroczkowski, Michael L. Gross, Daryl E. Giblin, and Robert J. Poreda (1994). "Incorporation of helium, neon, argon, krypton, and xenon into fullerenes using high pressure". J. Am. Chem. Soc.116 (5): 2193–2194. doi:10.1021/ja00084a089 .