STRUCTURAL STUDIES OF ADSORBED AND COADSORBED MOLECULAR-SPECIES

A short review is presented of the techniques of backscattering photoelectron diffraction and normal incidence standing X-ray wavefield absorption in the particular context of applications to the study of the local adsorption structure of molecular species on surfaces, including cases of coadsorption. Specific examples of NO and NO/O coadsorption on Ni(111), methoxy on Al(111) and PF3 on Ni(111) are used to illustrate the ability of these methods to obtain local structural information in situations of especial interest in understanding structural effects in surface reactions. Further developments of these methods to the study of vibrational anisotropies of adsorbed species (such as that associated with the wagging vibrational mode of atop adsorbed NH3 and PF3 on Ni(111)), and in the use of photoemission core level (''chemical'') shifts to study more complex problems, are described