Iodine chemistry is implicated in atmospheric chemistry and can form several oxides such as HOI, I₂, IO, OIO, and finally I₂O₅ or HIO₃, which may nucleate as nanoparticles relevant for cloud formation in remote environments. These oxides can be formed through reaction with oxidants or other halogen compounds in the gas phase or the particle phase. Most of the iodide oxidation processes have been suggested to be enhanced at interfaces, similar to other halogen species, either due to the surface propensity of intermediates or the iodine species itself. However, no data are available about the surface concentration of iodine species other than iodide. After two decades of research into the surface propensity of iodide and bromide, the picture emerges that their surface propensity is not as extreme as initially thought.
Liquid jet X-ray photoelectron spectroscopy (XPS) experiments have been carried out at the SIM beamline at the Swiss Light Source. Acquisition of kinetic energy dependent (thus at different probing depth) I3d, I4d core level and valence level spectra has been done for iodide, iodate and iodic acid. This allows to retrieve the surface propensity of these iodine species at the aqueous solution – air interface. Theoretical computations were performed to calculate the spectra using the so-called Frozen Embedding Method where DFT SAOP is coupled with CVS-EOM-IP-CCSD/d-aug-dy-all.ac2vz via a molecular mean-field X2C including the Gaunt interaction. The computation of the iodide core binding energies in the aqueous have been determined and compared to experimental measurements.