The Neutralization of HeC in the Gas Phase: Compelling Evidence for the Existence of an Endohedral Structure for He@C60

Neutralization‐reionization mass spectrometry was used to show that for both neutral He@C 60 and He@C , the noble gas atom is incorporated within the fullerene cavity. The C 60 H ˙+ ions were generated by high‐energy collisions of C with quasi‐stationary 4 He target atoms and cleaved in the mass spectrometer by loss of C 2 or multiples thereof, as is usual for endohedral MC 60 complexes.