Electron collisions with cyanoacetylene HC 3 N : Vibrational excitation and dissociative electron attachment

We experimentally probe electron collisions with ${\mathrm{HC}}_{3}\mathrm{N}$ 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 ${\ensuremath{\pi}}^{*}$ resonances are visible in the excitation of all the vibrational modes; however, broad ${\ensuremath{\sigma}}^{*}$ resonances are visible only in certain bond-stretching vibrational modes. The lower ${\ensuremath{\pi}}^{*}$ 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, 035201 (2015)]; however, approximately a factor of two difference is found in the absolute values.