The decay of the C 1s -> 2 pi (II)-I-3 inner-shell excited state of CO

Electron impact has been used to excite dipole forbidden inner-shell transitions of CO which are not accessible by photon impact. Coincidence techniques have then been used to study the decay of the C 1s-2pi (triplet PI) inner-shell excited state, and to isolate this autoionization spectrum from that of the (singlet PI) inner-shell excited state. An ab initio multiconfiguration and multicentre calculation allowed the assignment of the spectral features to the various participator and spectator transitions leading to the final CO+ doublet and quartet states. Although the same doublet states are populated from both the singlet and triplet intermediate states, the experimental intensities and energies are significantly different due to Franck–Condon effects.