Two-electron photoionization of endohedral atoms

Using He@C-60 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 sigma(++)(omega)/d epsilon. We found that at high photon energy prominent oscillations appear in it due to reflection of the second slow electron wave on the C-60 shell, which dies out at relatively high epsilon values, of about 2-3 two-electron ionization potentials. The results were presented for ratios R-C60(omega,epsilon)equivalent to d sigma(++)(omega,epsilon)/d sigma(a++)(omega,epsilon), where d sigma(a++)(omega,epsilon)/d epsilon is the two-electron differential photoionization cross section. We have calculated the ratio R-i,R-ful=sigma(++)(i)(omega)/sigma(a++)(i)(omega), that accounts for reflection of both photoelectrons by the C-60 shell. We have also calculated the value of two-electron photoionization cross section sigma(++)(omega) and found that this value is close to that of an isolated He atom. Results similar to He@C-60 are presented for He@C-70 and He@C-76.