ESDIAD (Electron Stimulated Desorption Ion Angular Distribution) Studies of the Structure of Species Chemisorbed on Ni(110). The Surface Bonding of NH3, NH2, and CO

摘要

In this paper it will be shown that ESDIAD (Electron Stimulated Desoption Ion Angular Distribution) can give detailed information about both the structural and the dynamic behavior of surface species. There are at present few physical measurement techniques in surface science which give such detailed information about surface bonding in polyatomic adsorbates. We have investigated the process: NH3(ads) yields > NH2(ads) + H(ads). Here, the NH3 molecule is found to bond by an electron donor mechanism to the ridge atop sites of the corrugated Ni(110) surface, and to exhibit either no preferential azimuthal orientation, or essentially free rotation. For temperatures as low as 29K, a halo H+ pattern is observed, indicating that the barrier to NH3 rotation is below about 0.07 eV. In contrast, the NH2 species is frozen azimuthally on the surface with its plane perpendicular to the Ni rows, yielding two sharp H+ beams in ESDIAD. This surface bonding mode is consistent with the molecular orbital structure of NH2. The NH2 species is thermally stable to about 375K.