We consider a two-dimensional gas of colliding charged particles confined to
finite size containers of various geometries and subjected to a uniform
orthogonal magnetic field. The gas spectral densities are characterized by a
broad peak at the cyclotron frequency. Unlike for infinitely extended gases,
where the amplitude of the cyclotron peak grows linearly with temperature, here
confinement causes such a peak to go through a maximum for an optimal
temperature. In view of the fluctuation-dissipation theorem, the reported
resonance effect has a direct counterpart in the electric susceptibility of the
confined magnetized gas