Electron dynamics of Cs anti-bonding surface state on copper

Electron dynamics induced by direct photoexcitation of the anti-bonding sta te on Cs/Cu(111) and Cs/Cu(100) are studied by the interferometric time-res olved two-photon photoemission. Femtosecond resolution pump-probe correlati on measurements indicate a lifetime of the Cs anti-bonding state of 50 fs o n Cu(111) at 50 K, while for Cu(100) only an upper limit of 5 fs can be est imated. Below the Ca antibonding peak maximum for Cs/Cu(111), the populatio n relaxation is non-exponential and appears to have a delayed rise which mo ves to longer delay times for lower probe energies. The population dynamics of the unoccupied state suggests a dissociative motion of Ca atoms leading to the photostimulated desorption.