HALOCARBON ADSORPTION ON FE(100) - ADSORPTION OF CBR4 STUDIED BY AES, LEED, WORK FUNCTION CHANGE AND THERMAL-DESORPTION - COMPARISON OF CBR4 WITH BR2 AND CCL4 BEHAVIOR

Carbon tetrabromide adsorbs dissociatively on Fe(100). The sticking probability remains constant from zero to θ > 0.9, indicating the existence of a long lived, mobile pre-cursor state. The work function increases on adsorbing CBr4, reachng a maximum value of Δø = 0.95 ± 0.02 eV at saturation. The diffraction pattern formed by room temperature adsorptionn is a (2 sin α′ × 2 sin α′)Rα′ structure. This is the same as the structure already observed for Br2 adsorption on Fe(100). Heating the saturated surface causes the adsorbed carbon to diffuse into the bulk. On further heating (which brings about a decrease in bromine concentration), the surface behaves in exactly the same way as Br2/Fe(100) under the same conditions. Adsorption of CBr4 on the saturated surface, at room and elevated temperatures, after removal of carbon by heating, and adsorption of Br2 on the saturated surface before and after removal of the carbon, have also been studied. The behaviour is shown to be consistent with the models used for Br2 adsorption. The carbon from the dissociated molecule is assumed to lie deep in the four-fold sites while the larger bromine atoms sit high on the surface and dominate the surface structure. Comparisons are drawn between the CBr4 and CCl4 adsorption systems. © 1979.