ADSORPTION OF CHLORINE ON THE PT(100) FACE - STRUCTURAL ASPECTS AND DESORPTION-KINETICS

The interaction of chlorine with the Pt(100) single crystal face has been studied using LEED and thermal desorption mass spectrometry. Cl2 molecules adsorb readily on the initially clean reconstructed Pt(100)-hex surface to form a chemisorbed adlayer. Adsorption of chlorine effects the removal of surface reconstruction which is completed at about 4 × 1014 Cl atoms/cm2. At higher concentrations a c(2 × 2) structure is formed. Beyond saturation of the c(2 × 2) structure the rate of further chlorine adsorption is largely diminuished. Eventually a (2 × 3) structure develops after heating to 500 K., corresponding to the limiting observed chlorine to platinum surface atom ratio of 2 3. In this stage the adlayer is interpreted to consist of a distorted hexagonal arrangement of adsorbed chlorine atoms, which are in part out of registry with the substrate. Temperature programmed thermal desorption is observable from 580 to 1100 K and yields exclusively Cl atoms and Cl2 molecules. The desorption kinetics is influenced by the coverage dependent desorption energy and by the substrate reconstruction taking place during desorption. A kinetic model encompassing surface diffusion of Cl atoms, substrate reconstruction and atomic and molecular desorption was proven by calculating desorption traces on the basis of a lattice gas model with lateral repulsive interactions using Monte Carlo simulations as well as an analytical treatment. © 1990.