Electron impact studies of autoionizing states in CO2 using a multi-angle parallel detection electron spectrometer

Abstract

The MAPDESS, a multi-angle-detector electron scattering spectrometer, has been adapted to electron ejection measurements. A study of autoionization from Rydberg states has been carried out for the neutral linear molecule CO2 in the continuum region 15–19 eV by low-energy electron impact. Observations have been made of structure due to excitation of these states by slow electron scattering and their decay by ejection of electrons. A multi-angle parallel detection technique has been used and this has enabled some CO2 autoionizing states resulting from non-dipole transitions to be observed clearly. The major features appearing in the ejected electron spectra of CO2 have tentatively been classified and (or) assigned in terms of autoionization to the ground ionic state X, from highly excited electronic states corresponding to the "Tanaka progression I" and "Tanaka–Ogawa" Rydberg series converging to the ionic A state, as well as from the Henning "sharp" and "diffuse" series, along with the forbidden npσu series, converging to the B state. In addition to the features already known, new features have been observed, and they seem to be rather sensitive to electron impact energies employed. Strong relative intensity variations are observed at the different impact energies, and marked angular effects are also found in the ejected electron spectra.