COVERAGE DEPENDENCE OF THE KINETICS FOR H-2 DESORPTION FROM RH(111)

Coverage-dependent sticking probabilities and second-order rate consta nts for recombinative desorption of hydrogen from Rh(111) have been me asured using molecular beam relaxation spectroscopy (MBRS) and time-re solved specular helium scattering. The sticking probability follows se cond-order Langmuir coverage dependence, with s(0) equal to 0.01 +/- 0 .005. Under isothermal and nearly isosteric conditions over the covera ge range 0.2-0.7 ML, the second-order rate constant for desorption is essentially independent of hydrogen coverage, in contrast to kinetic p arameters determined from thermal desorption spectra.