X-ray photoemission from mercury in vapor and condensed phases

The $4f$ ionization potentials for mercury in the vapor phase have been measured relative to the vacuum level; those for mercury condensed on gold, silver, and copper have been measured relative to the Fermi level. Correction for the work function of the solids, determined in a separate experiment, gives the ionization potentials of the condensed mercury relative to the vacuum. The vapor-phase ionization potentials are greater than those for condensed phases by 3.3 eV for $f_{\frac{7}{2}}$ electrons and 3.0 eV for $f_{\frac{5}{2}}$ electrons; these differences are nearly independent of the substrate. This shift is attributed to extra-atomic relaxation energies. Two models, a localized electron (exciton) model and an equivalent-cores thermochemical model, predict relaxation energies for these and other systems with reasonable accuracy. The splitting between the $f_{\frac{7}{2}}$ and $f_{\frac{5}{2}}$ levels is 4.01 eV in the gas phase and 3.7 eV in the solid phase. The change in splitting on condensation may be due to energy-loss phenomena peculiar to the surface.