Adsorption structure of CO on Pd (111) films and measurement of desorption energy of CO from the films

Abstract

Pd (111) films were grown on mica by vapor deposition in ultra-high vacuum. Adsorption structure of CO on the surface of the films was investigated by LEED. When the Pd surface was exposed to CO at room temperature, the LEED pattern changed from the 1 × 1 original pattern of the clean Pd surface to a superlattice pattern c (4 × 2) with broad spots. The superlattice structure was completed with an exposure of 10 l of CO. After saturated coverage of CO on the Pd film was obtained, measurement of the isothermal desorption was carried out using Auger electron spectroscopy (AES). AES peak-to-peak heights as a function of time were measured on the surface, kept at constant temperatures of 90–130°C. The data were analyzed using first-order kinetics, and as an activation energy for desorption of CO from the Pd surface, a value of 24.0 ± 0.3 kcal mol −1 was obtained.