Electronic relaxation of alkali metal atoms on the Cu(111) surface

Interferometric time-resolved two-photon photoemission measurements are performed on Cs and Rb chemisorbed on Cu(111). The population decay of the alkali-atom-induced anti-bonding state at 35 K is observed on 50 fs and 20 fs time scales for Cs and Rb respectively. Factors that contribute to such unusually long lifetimes, and in general determine the lifetimes of adsorbates on metal surfaces, are discussed in light of related measurements by Bauer et al. [Phys. Rev. B, 60 (1999) 5016] and theoretical simulations by Borisov et al. [Surf. Sci. 430 (1999) 165].