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 dσ⁺⁺(ω)/dɛ . 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 ɛ values, of about 2-3 two-electron ionization potentials. The results were presented for ratios R_C60(ω,ɛ)≡dσ⁺⁺(ω,ɛ)/dσ^a++(ω,ɛ) , where dσ^a++(ω,ɛ)/dɛ is the two-electron differential photoionization cross section. We have calculated the ratio R_i,ful=σ_i⁺⁺(ω)/σ_i^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 .