SYMMETRY SELECTION-RULES VS VIBRONIC COUPLING IN RESONANT SELECTIVE VIBRATIONAL-EXCITATION OF POLYATOMIC-MOLECULES BY ELECTRON-IMPACT

In the unsaturated polyatomic molecule series: C6H6, C2H4, CH3CHO, H2CO, (CE3)2CO, CH2CHCHCH2, C2H2, HCN and CH3CN, all presenting an overlap between a low energy π{black star} (1-2 eV) and a very broad σ{black star} (4-8 eV) shape resonance, we show that the vibronic coupling process between the π{black star} and the σ{black star} resonances can explain the resonant excitation of the non-totally-symmetric vibrational modes without invoking an s(l=0) wave in the scattering process. © 1990.