Photoionization of two-shell endohedral atoms

The photoionization of a two-shell endohedral A@C_N1@C_N2 is considered. Formulas are presented for cross sections and angular anisotropy parameters, both dipole and nondipole. The effect of the fullerenes shell upon photoelectron from atom A is taken into account substituting the action of the fullerene by two zero-thickness “bubble potential.” The fullerenes shells polarization is included assuming that the radius of the outer shell R₂ is much bigger than the inner R₁ and both much exceed the atomic radius r. This permits to express the effect via C_N1,N2 polarizabilities, which are connected to their photoionization cross sections. The interaction between shells C_N1 and C_N2 is taken into account in the random phase approximation (RPA). The effect of photoelectron scattering by both “bubble potentials” is included in the lowest order and in the RPA frame. As concrete examples, two endohedrals Ar@C₆₀@C₂₄₀ and Xe@C₆₀@C₂₄₀ are considered. In the Ar@C₆₀@C₂₄₀ case we consider 3p and 3s, while in the case Xe@C₆₀@C₂₄₀ 5p, 5s and 4d subshells are considered. A whole variety of peculiarities are found that deserve experimental verification.