  We investigate the kinetic-energy spectrum of electrons emitted from an
excited many-electron system, often called photo-electron spectrum (PES). We
are particularly interested on the impact of resonant modes of the system on
PES. To this end, we consider three systems with strong resonances, a Mg atom,
the small alkaline cluster ${{\rm K}_9}^+$, and the small carbon chain C$_3$.
To avoid dominant frequencies in the excitation process, we consider a
collision with a fast ion which is realized by an instantaneous boost of the
valence electrons, a process which excites all frequencies with equal weight.
The electron dynamics is investigated from a theoretical perspective using
time-dependent density-functional theory augmented by an average-density
self-interaction correction. We observe patterns which are similar to PES
usually obtained after irradiation by a laser pulse, in particular the
appearance of clear peaks. We show that these patterns are driven by strong
resonance modes of the system. Resonances are thus found to be another source
of peaks in the PES, besides photons (when present) with definite frequencies.
