Molecular single photon double K-shell ionization

We have studied single photon double K-shell ionization of small molecules (N2, CO, C2H2n (n = 1-3), …) and the Auger decay of the resulting double core hole (DCH) molecular ions thanks to multi-electron coincidence spectroscopy using a magnetic bottle time-of-flight spectrometer. The relative cross-sections for single-site (K−2) and two-site (K−1K−1) double K-shell ionization with respect to single K-shell (K−1) ionization have been measured that gives important information on the mechanisms of single photon double ionization. The spectroscopy of two-site (K−1K−1) DCH states in the C2H2n (n = 1-3) series shows important chemical shifts due to a strong dependence on the CC bond length. In addition, the complete cascade Auger decay following single site (K−2) ionization has been obtained.