WAVELENGTH DEPENDENCE OF THE PHOTOCHEMISTRY OF O2 ON PD(111) AND THE ROLE OF HOT-ELECTRON CASCADES

The photochemistry of 02 adsorbed on Pd (111) has been studied as a function of the energy of the exciting photons in the range of hv = 3.9-6.4 eV. The obtained data are reproduced by a proposed kinetic model considering photostimulated desorption and dissociation, whereby the latter gives rise to additional displacement processes. This modeling yields rate constants and, hence, cross sections for the respective processes. It is found that the cross sections for all processes rise exponentially with photon energy. This result motivates a study of the distribution of hot electrons generated by laser irradiation, and its decay via electron-hole pair scattering events resulting in a broad secondary electron distribution. The energetic and spatial distribution of these electrons is calculated. The probability for these electrons to tunnel into an adsorbate affinity level is modeled and compared to the observed photo cross sections.