Vibrationally selective resonant Auger spectroscopy of the3pcore-to-Rydberg excitation in CO

The Auger decay of the C $1s\to 3p$ excitation in CO has been studied by means of vibrationally selective angle-resolved electron spectroscopy. It is shown that for these highly excited Rydberg states the strict spectator model works excellently in describing the Auger decay. Consequently, all the spectral features have been identified by comparison to previous normal Auger studies. Intense lines belonging to $3p\to 4p$ shakeup also accompany the main lines; together with the total absence of any participator contribution, this reveals the atomiclike nature of the $3p$ Rydberg orbital. Remarkably large differences between the decay spectra recorded on the $3p({\upsilon }^{\prime }=0)$ and the $3p({\upsilon }^{\prime }=1)$ resonance reveal the spatial differences in the decay paths. For transitions to the final state with the lowest binding energy in the spectator region, an angular anisotropy dependent upon the vibrational quantum number of the final state is observed. We observe different angular anisotropy for transitions to different vibrational levels of the same electronic final state in resonant Auger spectroscopy.