Adsorbate effects on photoemission from Ag

We have used pyridine and a number of related molecules to lower the workfunction of thin Ag films so as to compare the effects of various molecular properties on the photoemission process and on surface electronic modes. We find that a nitrogen lone pair electronic orbital is essential for a large threshold shift. Other molecular properties, such as dipole moment and polarizability have a very small effect. The films are rough, therefore we see strong photoyields at the energy of the surface plasma mode, 3.6 eV. There is also a peak in the photoyield at 3.85 eV, the energy of the bulk plasmon.