Resonance phenomena observed in electron scattering from acetylene

Electron scattering from acetylene has been studied at low energies by means of an electron impact spectrometer. The 2.5 eV Pi g resonance was seen to lead to appreciable excitation of the nu 4 bending mode and the observed angular dependences of the scattered electrons could only be reconciled with angular correlation theory by assuming a bent geometry for this resonance and consequently a lowering of the molecular symmetry. A 2 Sigma +g resonance was located at 6 eV and is the analogue of that observed in isoelectronic N2 at 8 eV. Further information has been obtained on the Feshbach resonance series and assignments have been proposed based on the grandparent model.