A photoemission study of some liquid simple metals and alloys.

Measurements of the work function, quantum yield and low energy (6.oev hy 21.2eV) photoelectron spectra are presented for the simple metals In, A1, Pb, and Sn in the liquid and frozen solid states, and for Hg and the mercury alloys Hg5-In5, Hg75-In25, Hg96-Na04 In the liquid states only. The results obtained for the solid simple metals are consistent with other published results. The results for the liquid are very similar to those for the solid and are constant over a broad temperature range above the melting point. A Monte Carlo simulation of the photoemission process, based on the 3-step model of Berglund and Spicer, has been developed and used to examine the effects of variation of the electron-phonon scattering length on the quantum yield and escape depth of the photoelectrons. This programme has been used in conjunction with an analytical programme, based on the work of Krolikowski, to derive optical density of valence states functions and electron-electron scattering lengths for the liquids. In all cases the optical density of states functions show much stronger structure than expected on the basis of a weak scattering description of the liquid system and agree better with theoretical predictions for the solid, indicating that some aspects of the solid state band structure persist on melting. No evidence for conservation of the momentum vector k or for non-constant matrix elements is observed. In the case of mercury and the mercury alloys the results obtained agree well with the pseudogap concept proposed by Mott.