Coverage dependence of the kinetics for H-2 desorption from Rh(111)

Coverage-dependent sticking probabilities and second-order rate constants for recombinative desorption of hydrogen from Rh(111) have been measured using molecular beam relaxation spectroscopy (MBRS) and time-resolved specular helium scattering. The sticking probability follows second-order Langmuir coverage dependence, with s(0) equal to 0.01 +/- 0.005. Under isothermal and nearly isosteric conditions over the coverage range 0.2-0.7 ML, the second-order rate constant for desorption is essentially independent of hydrogen coverage, in contrast to kinetic parameters determined from thermal desorption spectra.