PHOTODESORPTION OF NO FROM AG(111) AND CU(111)

The adsorption, thermal reactions, and photoreactions of NO on Ag (111) and Cu(111) at 80-85 K have been studied by thermal-desorption spectroscopy (TDS), high-resolution electron-energy-loss spectroscopy (HREELS), and photon-induced desorption. Adsorption of NO on both surfaces is quite complicated. At saturation coverage, a number of chemical species are present, including atop and bridge-bonded NO, atomic N and O, and N2O. Photodesorption of NO, N2, and N2O is observed simultaneously under low-power photon irradiation in the wavelength range for 260-600 nm. From TD and HREEL spectra before and after photon irradiation, it is established that on both surfaces the atop NO is photoactive. Photon polarization, power-, and wavelength-dependences studies indicate that the mechanisms for photodesorption are nonthermal. A substrate-mediated mechanism involving photogenerated carriers at low photon energies (< 3 eV) and a direct excitation mechanism of the adsorbate-surface complex at high photon energies are used to explain the observed photodesorption.