  With an eye on dust particles immersed into an ionized gas, we study the
effect of a negative charge on the scattering of light by a dielectric particle
with a strong transverse optical phonon resonance in the dielectric constant.
Surplus electrons alter the scattering behavior of the particle by their phonon
limited conductivity in the surface layer (negative electron affinity) or in
the bulk of the particle (positive electron affinity). We identify a
charge-dependent increase of the extinction efficiency for low frequencies, a
shift of the extinction resonance above the transverse optical phonon
frequency, and a rapid variation of the polarization angles over this
resonance. These effects could be used for non-invasive optical measurements of
the charge of the particle.
