X-ray photoelectron spectroscopic studies of some iodine compounds

A number of iodine compounds are studied as solids, in particular some iodine-oxygen and iodine-chlorine compounds and the tri-iodide ion. The chlorine 2p electron binding energy for I2Cl6 can be resolved into two peaks of intensity ratio 2:1 corresponding to terminal and bridging chlorine atoms. The iodine 3d electron binding energy for the tri-iodide ion may be resolved into peaks corresponding to different iodine atoms. The experimental results are compared with CNDO calculations, using both a 5s, 5p(sp model) and a 5s, 5p and 5d(spd model) basis set, in the framework of the ground and relaxation potential models (GPM and RPM). The CNDO calculations (spd model) give good agreement with previously published charges for xenon compounds, and the spd model, but not the sp model, is found to give good agreement with the experimental results for iodine compounds. The RPM model is found to be an improvement over the GPM model. The overall bond orders obtained with the spd model charges and charges based on Pauling electronegativities are compared for the isoelectronic series SiO4–4, PO3–4, SO2–4, ClO–4, and the trends found to be in the opposite directions. For ClO–4, Pauling charges give particularly poor agreement with experiment.