Chemical dependence of core-level linewidths and ligand-field splittings: High-resolution core-level photoelectron spectra of I 4dlevels

High-resolution I 4d photoelectron spectra (total instrumental resolution 0.06 eV) of several iodine molecules, ICl, IBr, I₂, and Ch₂{I}₂$, are reported. The inherent I 4d Lorentzian linewidths increase in the above order, due to the decrease in electronegativity of the moieties bound to I. The ligand-field splitting as measured by the ${C}₂⁰$ crystal-field term decreases in the above order, and correlates extremely well with the electric-field gradient measured by $¹²⁹I$ quadrupole splittings.