IODINE ADSORPTION ON CLEAN AND CESIATED W(110) STUDIED WITH UPS AND METASTABLE IMPACT ELECTRON-SPECTROSCOPY (MIES)

Photoemission spectra (UPS with HeI) and metastable impact electron sp ectroscopy (MIES with He(1s2s)) are reported for the adsorption of io dine alone, the coadsorption of iodine and cesium, and the adsorption of CsI on W(110) at room temperature. It is demonstrated that the I(5p ) ionization is sensitively dependent on the chemical environment of t he iodine adsorbate. For iodine in a strong external field, such as fo r adsorption on clean metals, the photoemission spectra reflect the St ark splitting of the (5p) orbital while the MIES spectra are due to th e Auger capture process. When adsorbed near to cesium iodine feels a c omparatively weak external field and the emission spectra both for UPS and MIES (due to the Anger deexcitation process) reflect the I(5p) fi nestructure splitting in the final state after the emission process.