An experimental and theoretical investigation of the valence double photoionisation of the iodine molecule

The double photoionisation spectrum of molecular iodine has been measured at three wavelengths by the TOF-PEPECO technique and is interpreted using relativistic molecular structure COSCI calculations of potential curves for a large number of electronic states connected to the three lowest groups of dissociation limits. The lowest double ionisation energy is 24.85 ± 0.02 eV (adiabatic) or 24.95 ± 0.02 eV (vertical). It is associated with the 3Σg,0- electronic state of I22+. The double ionisation process is mainly direct, and positions and widths of the bands are well reproduced by the calculations.