An optical differential reflectance study of adsorption and desorption of xenon and deuterium on Ni(111)

We studied adsorption and desorption of Xe and deuterium on Ni(111) using an optical differential reflectance technique. The main findings are: (i) the differential reflectance varies almost linearly with the surface densities of deuterium and Xe adatoms, and the signals can be described well with a three-layer model and the known dielectric responses of the surface layers: (ii) the adsorption of deuterium atT = 120 K follows the Langmuir kinetics, while the adsorption of Xe atT = 38 K follows the zeroth-order kinetics; (iii) nearT = 70 K, the rate of Xe desorption is almost coverage-independent with an activation energy ofE _des = 4.4 ± 0.2 kcal/mol. Our analysis suggests that the Xe desorption is likely to be dominated by the escape rate from the corners of two-dimensional Xe islands.