  We show, with an example of Na_92, that for jellium metal clusters the
interference of fast electron-waves emitted from equivalent sites on the
cluster edge produces monochromatic oscillations in all photoionization
observables as a function of the photoelectron momentum; the effect is
equivalent to the usual dispersion phenomenon. In dealing with formalisms, a
serious consequence of the inadequacy of self-interaction corrected local
density-functional theory in correctly accounting for the exchange interaction
is identified. We also briefly discuss the influence of the ionicity of the
residual core on photospectra by considering the neutral member with N=58 and
and the ionic member with N=52 of the Na_58 iso-jellium series, where N is the
number of valence electrons. A few final remarks on possible implications of
these results on other quantum systems of delocalized electrons are made.
