Electronic excitation of carbon dioxide in the 10.5-18 eV range studied by inelastic electron scattering spectroscopy

Electronic excitation of carbon dioxide has been studied in the 10.5-18 eV energy range by electron impact energy-loss spectroscopy. The experimental conditions (various impact energies ranging between 60 and 1.35 eV above thresholds and various detection angles between 4 and 50') enabled the authors to show evidence for most of the g to or from g forbidden transitions predicted by theoretical calculations to lie in the same region as the Rathenau progressions. The first three members of four new Rydberg series converging to the ionic ground state have been identified, two being triplets and the two others being symmetry-forbidden. In addition, the symmetry-forbidden character of two series, one converging to the A 2 Pi u state and the other to the B 2 Sigma u state, has been obtained experimentally; the triplet component of the 2 pi u to 3p sigma u transition is observed with a singlet-triplet splitting of 0.26 eV.