The influence of oxygen on the interaction of CCl 4 with Fe(110) — titration of defect sites with oxygen

Abstract

Competition between two active adsorbates, O 2 and CCl 4, on Fe(110) has been investigated using temperature programmed desorption, Auger spectroscopy, and reaction kinetic methods. It is found that preadsorbed oxygen decreases the tendency for CCl 4 to dissociate. A portion of this effect has to do with the titration of defect sites on the Fe(110) crystal which are especially active for promoting CCl 4 dissociation. Surprisingly, the production of FeCl 2 is enhanced in the presence of chemisorbed oxygen and the desorption temperature for FeCl 2 is also increased. Competitive adsorption kinetic experiments at 325 K, using mixed effusive beams of CCl 4 and O 2, show that the reaction probability of CCl 4 at low coverages remains at unity for all gas mixtures studied. In contrast to CCl 4 behavior, the reaction probability of O 2 at low coverages is significantly decreased in the presence of CCl 4. The negative effect of CCl 4 adsorption on oxygen adsorption capacity is more dramatic than the negative effect of oxygen adsorption on CCl 4 adsorption capacity at 325 K.