Vacancy decay in endohedral atoms: the role of an atom's non-central position

We demonstrate that the Auger decay rate in an endohedral atom is very sensitive to the atom's location in the fullerene cage. Two additional decay channels appear in an endohedral system: (a) the channel due to the change in the electric field at the atom caused by the dynamic polarization of the fullerene electron shell by the Coulomb field of the vacancy and (b) the channel within which the released energy is transferred to the fullerene electron via the Coulomb interaction. The relative magnitude of the correction terms is dependent not only on the position of the doped atom but also on the transition energy ω. Additional enhancement of the decay rate appears for transitions whose energies are in the vicinity of the fullerene surface plasmons energies of high multipolarity. It is demonstrated that in many cases the additional channels can dominate the direct Auger decay resulting in pronounced broadening of the atomic emission lines. The case study, carried out for Sc2+-C6-80, shows that narrow autoionizing resonances in an isolated Sc2+ within the range ω = 30-45 eV are dramatically broadened if the ion is located strongly off the centre. Using the developed model, we carry out the quantitative analysis of the photoionization spectrum for the endohedral complex Sc3N-C80 and demonstrate that the additional channels are partly responsible for the strong modification of the photoionization spectrum profile detected experimentally by Mueller et al (2007 J. Phys.: Conf. Ser. 88 012038).