Vibrationally resolved decay spectra of CO at the C and O K-edges: experiment and theory

The resonant Auger spectrum of CO has been measured at both the C and O K-edges. At the C 1s->2pi resonance the decay spectrum was recorded selectively at the energies of the = 0, 1 and 2 vibrational states. Vibrational fine structure was not only resolved on the participator but also on the spectator lines. For the O 1s->2pi resonance the photon energy bandwidth was sufficiently low that different, vibrationally distinct regions of the absorption profile could be selected. Ab initio calculations and their detailed analysis are presented for both the C 1s->2pi and O 1s->2pi decay spectra. At the C 1s->2pi resonance the calculation explicitly accounts for the vibrational fine structure including vibrational-lifetime interference effects. The appearance of the spectator part of the spectrum is shown to be strongly influenced by the existence of unbound states and diabatic interactions. The nodal structure of the vibrational wavefunction of the core-excited state is reflected in the decay spectrum.