Threshold energy electron impact excitation of carbon dioxide and carbon disulphide

Abstract

The threshold energy electron impact excitation spectra of CO 2 and CS 2 have been studied using the sulfur hexafluoride scavenger technique. The main results are triplet state excitation and autoionisation of negative ions associated with resonant excited states of the molecules. This confirms previous data concerning diatomic molecules. Furthermore, transitions such as 1Π g−X 1Σ g + and 1Π u−X 1Σ g + are only weakly induced by low energy electrons, while the corresponding triplet excitations are probably more easily produced. Structures at 5.6, 6.1 and 6.6 eV observed in CS 2 are due to negative ions and/or to 3Π u, 3Π g excitation. The autoionisation of CO 2 −(X 2Π u) proceeds also by ejection of a thermal energy electron and leads to highly excited vibrational levels (3–5 eV) of the ground electronic state of CO 2.