Resonance-Enhanced Shakeup in Near-Threshold Core Excitation of CO andN2

Abstract
Auger and x-ray photoelectron spectroscopies indicate that the probabilities for 1π2π shakeup in the C 1s ionization of CO and for the 1πu1πg shakeup in N2 are about an order of magnitude greater near the threshold than at energies well above it (the sudden limit). This enhancement is attributed to a conjugate process that is strengthened by the intense core-to-π resonance just below the core-ionization threshold.