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

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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 4d3/2 and 4d5/2 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 E4d, generally increase as the ligand electronegativity increases. C20 also correlates well with the nuclear field gradient, eqn, 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 E4d, C20 and especially the linewidth.