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

TL;DR

This paper investigates how the position of an atom inside a fullerene cage affects its Auger decay rate, revealing new decay channels and their impact on spectral features, especially when the atom is off-center.

Contribution

It introduces a model showing the decay rate sensitivity to atom position and identifies additional decay channels influencing the spectrum of endohedral atoms.

Findings

Decay rates are highly sensitive to atom position within the fullerene.

Additional decay channels can dominate over direct Auger decay.

Off-center atoms cause significant broadening of autoionizing resonances.

Abstract

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 dynamic polarization of the fullerene electron shell by the Coulomb field of the vacancy, (b) the channel within which the released energy is transferred to the fullerene electron via the Coulomb interaction. % The relative magnitudes of the correction terms are dependent not only on the position of the doped atom but also on the transition energy $\om$. 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 over the direct Auger decay resulting in pronounced broadening of the atomic emission lines. % The case study, carried out for Sc$^{2+}$@C$_{80}^{6-}$, shows that narrow autoionizing resonances in an isolated Sc$^{2+}$ within the range $\om = 30... 45$ eV are dramatically broadened if the ion is located strongly off-the-center. % Using the developed model we carry out quantitative analysis of the photoionization spectrum for the endohedral complex Sc$_3$N@C$_{80}$ and demonstrate that the additional channels are partly responsible for the strong modification of the photoionization spectrum profile detected experimentally by M\"{u}ller et al. (J. Phys.: Conf. Ser. 88, 012038 (2008)).