Absolute angle-differential vibrational excitation cross sections for electron collisions with diacetylene

Abstract

Absolute vibrational excitation cross sections were measured for diacetylene (1,3-butadiyne). The selectivity of vibrational excitation reveals detailed information about the shape resonances. Excitation of the $\mathrm{C}\ensuremath{\equiv}$C stretch and of double quanta of the $\mathrm{C}\ensuremath{-}$H bend vibrations reveals a ${}^{2}{\ensuremath{\Pi}}_{u}$ resonance at 1 eV (autodetachment width $~$30 meV) and a ${}^{2}{\ensuremath{\Pi}}_{g}$ resonance at 6.2 eV (autodetachment width 1--2 eV). There is a strong preference for excitation of even quanta of the bending vibration. Excitation of the $\mathrm{C}\ensuremath{-}$H stretch vibration reveals ${\ensuremath{\sigma}}^{*}$ resonances at 4.3, 6.8, and 9.8 eV, with autodetachment widths of $~$2 eV. Detailed information about resonances permits conclusions about the mechanism of the dissociative electron attachment.