ELECTRONIC EXCITED-STATE OF NO ADSORBED ON CU(III) - A 2-PHOTON PHOTOEMISSION-STUDY

Two-photon photoemission was observed from molecularly adsorbed NO on Cu(111) at 110 K. Excitation and photoemission were performed with a laser light of 5 ns duration in the photon energy range from 3.8 to 4.5 eV. The NO-induced photoemission feature was found to be composed of two components: one was attributed to the sequential two-photon photoemission from the ground state of adsorbed NO, the other to the one-photon photoemission from the NO negative-ion state which was formed by hot electrons in the Cu substrate. The two-photon photoemission intensity from the ground state NO was resonantly enhanced at the photon energy of 3.98±0.05 eV. The photon energy dependence was attributed to resonance excitation to the excited state of adsorbed NO. Width of the resonance curve was 0.3 eV, suggesting that the lifetime of the excited state is around 2 fs. The negative-ion state of adsorbed NO was 1.26±0.07 eV above the Fermi level. The energy width of the photoemission feature from the negative-ion state was about 0.4 eV which was fairly narrower than those observed in the inverse-photoemission spectra. © 1995 American Institute of Physics.