Confinement resonances in the photoionization of endohedral atoms: myth or reality?

We demonstrate that the structure of confinement resonances in the photoionization cross section of an endohedral atom is very sensitive to the mean displacement < a > of the atom from the cage centre. The resonances are strongly suppressed if 2 < a > exceeds the photoelectron half-wavelength. We explain the results of recent experiments which contradict the earlier theoretical predictions on the existence of confinement resonances in particular endohedral systems.