Collisional fragmentation of Ar@C60

The fragmentation patterns resulting from collisions between (Ar@C60)+ or (Ar@C60)− ions and H2, He, CH4, Ne, Ar and Kr target gases have been measured. The ion-source material Ar@C60 was synthesized by heating C60 under 3000 atm of argon gas, leading to a 10−3 concentration of endohedral fullerenes. The fragmentation spectra (charged molecules only) are dominated by positive ions both when positive or negative endohedrals break up. Endohedral fragment ions Ar@Cn+ (48⩽n⩽60) as well as all carbon fragments are observed. For collisions involving (Ar@C60)−, ejection of the Ar atom together with two electrons, without permanently damaging the fullerene cage, is a prominent reaction channel, indicating that a `windowʹ or a deformation in the form of e.g. a large hole, through which the argon atoms can exit, is opened during the collision.