UV-LASERPHOTOCHEMISTRY OF MOLECULES ON SOLID-SURFACES - NO/NI(100)-O

We have studied the photochemistry of NO and NO2 on Ni(100) using 193 nm light from an excimer laser. The experiment is complete in the sense that we characterize the desorbing particles by their rotationally and vibrationally resolved time of flight spectra via LIF (Laser Induced Fluorescence)- and REMPI (Resonance Enhanced Multi Photon Ionization)- techniques in the gas phase, and we characterize the solid surface before and after irradiation by electron spectroscopic methods, i.e., AES, LEED, and XPS. We find the build up of NiO after irradiation of the molecular adsorbates. The structure of the oxide is characterized by LEED. The electronic and geometric structure of NO and NO2 adsorbed on NiO is studied using angle resolved photoelectron spectroscopy (ARUPS), electron energy loss spectroscopy (HREELS) and near edge x-ray absorption fine structure (NEXAFS) measurements and the results are compared with those for NO and NO2 on clean Ni(100). For the ARUPS and NEXAFS measurements we have used synchrotron radiation from the storage ring BESSY I in Berlin. As expected, on NiO the desorption process has a much higher cross section than on the clean metal surface. A "photodesorption" channel of NO desorbing from NiO is clearly identified by the rotationally resolved time-of-flight spectra. In addition to the photodesorption channel a "thermal" channel is observed. The influence of the change of the adsorbate's geometric and electronic structure on desorption will be discussed. © 1990 IOP Publishing Ltd.