Electronic-state energies of the CH₂I²⁺₂, CHI²⁺₃ and CI²⁺₄ dications

Abstract

The double-ionization energies of CH₂I₂, CHI₃ and CI₄ have been measured and calculated. Double-charge-transfer spectrometry was used in the experimental part of the investigation, and a modified multiple scattering Xa method was used to calculate the energies. In order to test the accuracy of the calculations, the computational method was initially applied to CH₃I; the values obtained were found to be in good agreement with those measured previously. Calculated data for CH₂I₂ indicate that a large number of electronic states of the dication exist. By forming appropriate groups of states, mean calculated double-ionization energies were obtained which agree with the measured data. For CHI₃ and CI₄, the number of states calculated to exist is considerably less. When groups need to be formed, the numbers in them are much less than those for CH₂I₂. Good agreement between grouped calculated data and those measured was obtained for CHI₃ and CI₄. The exception was the four lowest states of CI₄²⁺ which appear not to be populated experimentally. A probable explanation is that the endoergicities of the relevant double-electron-capture reactions are too low, lying outside the operative reaction window of endoergicities.