π resonance of chemisorbed alkali atoms on noble metals

We have performed a joint experimental and theoretical study of the unoccupied electronic structure of alkali adsorbates on the (111) surfaces of Cu and Ag. Combining angle- and time-resolved two-photon photoemission spectroscopy with wave packet propagation calculations we show that, along with the well known σ resonance oriented along the surface normal, there exist long-lived alkali-localized resonances oriented parallel to the surface (π symmetry). These new resonances are stabilized by the projected band gap of the substrate and emerge primarily from the mixing of the p and d Rydberg orbitals of the free alkali atom modified by the interaction with the surface.This work was supported by the U.S. Department of Energy Grant No. DE-FG02-03ER15434, Petroleum Research Fund (44158-ACS), Spanish MEC grant, the European FP6-NoE grant Nanoquanta. H. P. and V. M. S. acknowledge support from the IKERBASQUE foundation.Peer reviewe