ELECTRON-IMPACT STUDIES OF AUTOIONIZING STATES IN CO2 USING A MULTI-ANGLE PARALLEL DETECTION ELECTRON SPECTROMETER

The MAPDESS, a multi-angle-detector electron scattering spectrometer, has been adapted to electron ejection measurements. A study of autoion ization from Rydberg states has been carried out for the neutral linea r 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 appearin g in the ejected electron spectra of CO2 have tentatively been classif ied and (or) assigned in terms of autoionization to the ground ionic s tate X, from highly excited electronic states corresponding to the ''T anaka progression I'' and ''Tanaka-Ogawa'' Rydberg series converging t o the ionic A state, as well as from the Henning ''sharp'' and ''diffu se'' series, along with the forbidden np sigma(u), series, converging to the B state. In addition to the features already known, new feature s have been observed, and they seem to be rather sensitive to electron impact energies employed. Strong relative intensity variations are ob served at the different impact energies, and marked angular effects ar e also found in the ejected electron spectra.