Influence of acceptor and donor adsorbates (CO,K, NH3) on Pt surface core-level shifts

4f core-level shifts have been measured for clean surfaces of Pt(111), Pt(331), and Pt(557). Surface peaks due to terrace sites are shifted toward lower binding energy (0.32 ± 0.05 eV) from the bulk peak, whereas peaks from step atoms are shifted by 0.58 ± 0.05 eV also to lower binding energy. The intensity ratios for the two sites differ considerably between the stepped Pt surfaces. Chemisorption of carbon monoxide on the Pt(331) surface is preferential to step sites, with a Pt 4f binding energy shift of ～ 1.29 eV toward higher binding energy. Chemisorption of potassium and ammonia also produces Pt 4f surface shifts which are at higher binding energy than the bulk peak. These experiments do not support the concept of electron donation by these adsorbates into metal d orbitals. The results are discussed in view of, and supported by, tight-binding LCAOMO calculations of potassium and ammonia interacting with a Pt(111) thin film.