Autoionisation of doubly excited states in the C 1s photoexcitation of CO

The vibrationally resolved C 1s−1 main line in the photoelectron spectrum of CO has been investigated just above the C 1s ionisation threshold where the absorption cross section is characterized by sharp, intense doubly excited states. They decay in part via resonant Auger processes, but can also couple via autoionisation to the C 1s−1 continuum, causing striking changes in the vibrational fine structure. In some cases very high vibrational levels up to quantum numbers of ν′= 7 are populated.