Low-energy electron collisions with dichloromethane and butadiene: Selectivity of resonant vibrational excitation

Abstract

Vibrational excitation by electron impact via low-lying energy resonances has been investigated in butadiene and dichloromethane, focusing on the problem of the selectivity of this excitation. In dichloromethane, for the lowest resonances around 1.2 and 3.4 eV, the excitation of the CCl stretch mode ν 3(a 1) is dominant, in agreement with the selection rules. For trans-1,3-butadiene, CCC skeleton modes - particularly the CC ν 4 stretch mode - are strongly excited via the 2A u resonance. On the other hand, resonant vibrational excitation of these modes via the 2B g resonance around 3 eV appears only weakly due to the short lifetime of the anion state. Noticeable excitation of CH stretch modes is also observed and attributed to higher resonances. The major excitation cross sections versus electron energy along with their angular dependences are presented for both molecules.