High-resolution study of resonant decay following the O 1s->pi* excitation(s) in CO2: evidence for an overlapping Rydberg transition

Electronic decay spectra associated with the O1s -> 2pi_u (pi*) transition(s) in CO2 have been measured at several photon energies within the width of the primary excitation. Significant differences in the shape and relative intensity of the decay features allow the high-energy shoulder evident on the ?* absorption band to be identified as an overlapping Rydberg transition. This method requires the availability of a photon source with a very narrow bandwidth at the O K-edge.