Giant resonances of endohedral atoms

It is demonstrated for the first time that the effect of a fullerene shell on the photoionization of a caged atom in an endohedral can result in the formation of giant endohedral resonances or GER. This is illustrated by the concrete case of the Xe@C-60 photoionization cross section that, at 17 eV, exhibits a powerful resonance with total oscillator strengths of about 25. The prominent modification of the 5p(6) electron photoionization cross section of Xe@C-60 takes place due to the strong fullerene shell polarization under the action of the incoming electromagnetic wave and the oscillation of this cross section due to the reflection of the photoelectron from Xe by the C-60. These two factors transform the smoothly decreasing 5p(6) cross section of Xe into a rather complex curve with a powerful maximum for Xe@C-60, with the oscillator strength of it being equal to 25. We also present the results for the dipole angular anisotropy parameter that is strongly affected by the reflection of the photoelectron waves, but not modified by C-60 polarization.