Single-photon core-valence double ionization of molecular oxygen

Single-photon core-valence double ionization of molecular oxygen has been studied using a magnetic bottle time-of-flight electron coincidence spectrometer. The $K^{-1}{V}^{-1}$ double ionization electron spectrum of ${\mathrm{O}}_2$ is reported and is assigned with the aid of ab initio calculations. A direct comparison of the core-valence double ionization electron spectra with the conventional valence band photoelectron spectrum is made. The lowest core-valence double ionization energy is found to be $571.6\mathrm{eV}$ and is associated with a ${}^3\Pi$ dicationic state.