Resonances in photoionization cross sections of inner subshells of atoms inside the fullerene cage

A model for the calculation of photoionization cross sections of an atom inside the fullerene cage is proposed. In the frame of this model the M@C-60 endohedral is considered as an isolated M atom located in the centre of the spherically symmetrical fullerene shell. The potential of this shell is written as the Dirac delta function in the radial coordinate. On the basis of this model a comparative study of the photoionization cross sections of an isolated M atom and the same atom in M@C-60 is carried out. It is shown that near the thresholds of ionization of atomic subshells the resonance peaks appear in the photoeffect cross sections. The positions of these resonances on the scale of photoelectron energy are defined by the fullerene radius and the affinity energy of an electron to C-60 The general formulae derived are used to calculate the photoionization cross sections of the inner subshells of the He, Ne and Ca atoms inside the fullerene cage.