X-ray photoelectron spectroscopy of gaseous and solidI2: Ion-state-enhanced intermolecular interactions

Gas- and solid-phase x-ray photoelectron spectra of ${\mathrm{I}}_2$ are compared. The shake-up satellite structure on the core-level peaks for ${\mathrm{I}}_2$ in the gas phase can be interpreted using a one-electron model of electronic transitions among states of the molecular ion. In the solid phase, the shake-up transition energies are greatly increased owing to the dynamic nature of the photoionization process, which enhances the intermolecular interactions of the molecular ion with neighboring neutral molecules. Complete-neglect-of-differential-overlap-2 model molecular-orbital calculations have been used to interpret the spectra in terms of strong intermolecular interactions in the solid phase.