  Photoionization studies of Na20 and Na92 clusters are carried out in a
framework of linear response density functional theory. Cross sections show
substantial spillover of plasmon resonances to the near-threshold ionization
energies which are in reasonable agreements with measurements. The analysis of
the oscillator strength, consumed by the cross section, lends further insights.
The many-body interaction induced self-consistent field from density
fluctuations suggests the existence of an attractive force. This may cause
time-delayed plasmonic photoemissions in ultrafast measurements. At the waning
end of the plasmon structure, a strong minimum in the cross sections from a
correlation-driven coherence effect is predicted which can possibly be observed
by the photoelectron spectroscopy.
