Ejected-electron spectroscopy of autoionising states of CO using an electron-electron coincidence technique

Quantitative measurements have been made of the relative intensities for electron-emitting transitions from autoionising levels of carbon monoxide to vibrational levels of the ground electronic state of CO+, following electron impact excitation. An electron-electron coincidence technique was used, in which the scattered electrons which had excited a selected autoionising level, and ejected electrons resulting from subsequent autoionisation processes were detected in separate analysers. The measured intensities are compared with Franck-Condon calculations using Morse potentials to represent the autoionising levels and ion levels. The results obtained indicate that the equilibrium inter-nuclear separation for the autoionising levels is 1.243 + - 0.001 A, very close to that for the A 2PI state of CO+, which is the probable series limit. Previous assignments of the autoionising levels, based on photoabsorption and photoelectron spectra, are discussed in the light of the present results. (author)