Vibrationally selective resonant Auger spectroscopy in CO: evidence of thevalence character of the 3s 'Rydberg level'

Auger decay from the C 1s-(1)3s core-excited state of CO has been studied b y means of angular resolved vibrationally selective electron spectroscopy. It is observed that the so-called strict spectator model provides only a qu alitative description of the C 1s-(1)3s Auger decay. We interpret this as e vidence for a strong valence character of the 3s orbital. Transitions assig ned to the 3s --> 4s Anger shake-up are revealed. For transitions to the fi nal state with 5 sigma(-2)3s leading configuration, there are indications o f angular asymmetry which depend upon the vibrational level of the final st ate.