Influences from the C 1s shape resonance on the vibrational progression in the Auger decay of CO

Auger decay from the C $1s$ core-ionized state of CO has been studied with vibrational resolution both at the C $1s$ shape resonance and far above. Variations in the vibrational intensity distribution with photon energy are observed. This observation is explained solely by the modified vibrational envelope of the core-ionized intermediate state at the shape resonance maximum, as demonstrated in a numerical simulation. This implies that the temporary trapping of the photoelectron at the shape resonance does not significantly affect the deexcitation process. Thus the deexcitation step is described by the Franck-Condon principle even at the shape resonance. The angular anisotropy of the Auger decay at the shape resonance has also been studied with vibrational resolution. Weak dependence upon the final state and no detectable influence from the vibrational quanta is observed.