Photoemission Spectroscopy in the Presence of Adsorbate-Covered Surfaces

A theory of the ultraviolet photoemission spectroscopy of metals with adsorbate covered surfaces yields $\Delta j\left(\omega \right)\propto {G_{\mathrm{aa}}}^I(\omega -{\omega }_0)-D{G_{\mathrm{aa}}}^R(\omega -{\omega }_0)$. $\Delta j\left(\omega \right)$ is the excess current at the energy $\omega$ produced by the adsorbates, ${\omega }_0$ is the photon energy, $\left(\frac{1}{\pi }\right){G_{\mathrm{aa}}}^I$ is the density of states at the adsorbate, and ${G_{\mathrm{aa}}}^R$ is the real part of the Green's function at the adsorbate. $D$ is nonzero if $\omega -{\omega }_0$ is degenerate with the metal energy bands, and can be large ($D\sim 1$) for typical experimental conditions.