Ligand-field splittings and core-level linewidths in I 4d photoelectron spectra of iodine molecules

Abstract

High‐resolution I 4d photoelectron spectra (total instrumental resolution ∼0.06 eV) of seven simple iodine molecules, ICl, IBr, I₂, HI, CH₃I, CH₂I₂, and CF₃I, have been recorded. Ligand‐field splitting (as measured by the asymmetric C₂⁰ crystal‐field term) splits the 4d_3/2 and 4d_5/2 lines into a doublet and triplet, respectively. In contrast to Si 2p spectra, the I 4d spectra generally show little evidence for vibrational splitting or broadening. The C₂⁰ values, like the binding energies E_4d, generally increase as the ligand electronegativity increases. C₂⁰ also correlates well with the nuclear field gradient, eq_n, as measured by Mössbauer spectroscopy or nuclear quadrupole resonance. For the first time we have been able to study the chemical dependence of the inherent lifetime width of a core hole. We show that the I 4d linewidths generally decrease as the electronegativity of the ligand increases, and as the valence I 5p electron density decreases. We also show that there are large relaxation effects on E_4d, C₂⁰ and especially the linewidth.