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

The double valence photoelectron spectrum of ICl has been measured at two photon energies, 303.78 Å and 379.3 Å, by the TOF-PEPECO technique. Relativistic molecular electronic structure calculations have been performed for electronic states connected to the three lowest groups of dissociation limits to support the interpretation, and vibrational constants have been calculated for the quasi-bound states. The two lowest double ionisation energies are found to be 27.45 ± 0.1 eV (vertical) and 27.69 ± 0.1 eV (vertical). They are associated with the X3Σ0,1- electronic states of ICl2+, respectively, which are the only states predicted to be stable by the calculations. The two following states connected to the same configuration are in order a 1Δ2 and b 1Σ0+. The double ionisation processes building up the spectrum are found to be mainly direct, and energies and widths of the bands are well reproduced by the calculations.