Femtosecond dynamics of electronic excitations of adsorbates studied by two photon photoemission pulse correlation: CO/Cu(111)
E. Knoesel, T. Hertel, M. Wolf, and G. Ertl
Chem. Phys. Lett. 249, 409 - 416 (1995)
An equal pulse correlation technique based on angle resolved two-photon photoemission is employed to investigate the lifetime of electronic excitations of an adsorbate on a single crystal metal surface. Photoemission from an occupied surface state on Cu(111) by a non-resonant two-photon process via the sp-band gap is used to characterize directly at the surface the width and shape of 65 fs laser pulses at a photon energy of hv = 3.4 eV. The 2PPE correlation technique allows to establish an upper limit of t < 20 fs for the lifetime of the 2¼* resonance of CO adsorbed on Cu(111), whereas from the spectral width of the 2¼*-level a lower limit of ~1 fs is estimated.
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