Two-electron photoionization of endohedral atoms

Using He-C{sub 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}{sup ++}({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{sub 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{sub C{sub 60}}({omega},{epsilon}){identical_to}d{sigma}{sup ++}({omega},{epsilon})/d{sigma}{sup a++}({omega},{epsilon}), where d{sigma}{sup a++}({omega},{epsilon})/d{epsilon} is the two-electron differential photoionization cross section. We have calculated the ratio R{sub i,ful}={sigma}{sub i}{sup ++}({omega})/{sigma}{sub i}{sup a++}({omega}), that accounts for reflection of both photoelectrons by the C{sub 60} shell. We have also calculated the value of two-electron photoionization cross section {sigma}{sup ++}({omega}) and found that this value is close to that of an isolated He atom. Results similar to He-C{sub 60} are presented for He-C{sub 70} and He-C{sub 76}.