Two-electron photoionization of endohedral atoms

Using He@ C60 as an example, we demonstrate that the static potential of the fullerene core essentially alters the cross section of the two-electron ionization differential in one-electron energy d σ++ (ω) dε. We found that at high photon energy prominent oscillations appear in it due to reflection of the second slow electron wave on the C60 shell, which "dies out" at relatively high ε values, of about 2-3 two-electron ionization potentials. The results were presented for ratios R C60 (ω,ε) d σ++ (ω,ε) d σa++ (ω,ε), where d σa++ (ω,ε) dε is the two-electron differential photoionization cross section. We have calculated the ratio Ri,ful = σi ++ (ω) σi a++ (ω), that accounts for reflection of both photoelectrons by the C60 shell. We have also calculated the value of two-electron photoionization cross section σ++ (ω) and found that this value is close to that of an isolated He atom. Results similar to He@ C60 are presented for He@ C70 and He@ C76.