Coherence between the photoionization of different inner-shell vacancy states of argon

We have observed coherence between the photoionization of two different inner-shell vacancy states of argon, the energies of which differ by more than 75 eV. The method is based on the occurrence of interferences between photoelectrons and Auger electrons resulting from the photoionization of the two states concerned. The measured line shape of the interference structure can be well explained using the theory of van den Brink et al. on state-state interference. From the measurements we have derived a value of 1.9±{}0.2 for the width of the Ar 2s^-1{(}²S1/2) state.