  We experimentally probe electron collisions with HC$_3$N in the energy range
from 0 to 10 eV with the focus on vibrational excitation and dissociative
electron attachment. The vibrational excitation cross sections show a number of
resonances which are mode specific: the two dominant $\pi^*$ resonances are
visible in the excitation of all the vibrational modes, however, broad
$\sigma^*$ resonances are visible only in certain bond-stretching vibrational
modes. The lower $\pi^*$ resonance shows a pronounced boomerang structure.
Since it overlaps with the threshold peak originating from a long-range
electron-molecule interaction, the interference pattern is rather unusual.
Somewhat surprisingly, the boomerang structure is visible also in the elastic
scattering cross section. The dissociative electron attachment cross sections
agree qualitatively with the data of Gilmore and Field [J. Phys. B 48 (2015)
035201], however, approximately a factor of two difference is found in the
absolute values.
