ISOTOPES INTO THE Ru ( 0001 ) CRYSTAL SURFACE

The coadsorption of H 2 and D 2 on Ru(0001) has been studied by thermal programmed desorption. An inverse kinetic isotope effect comparing H2, HD and D 2 desorption has been observed with D 2 desorption being most rapid for temperatures above 350 K. This effect is attributed to a normal isotopic enhancement of H(ads) penetration into subsurface sites on Ru(0001) during the rapid temperature rise of 10 K s-1 following low-temperature adsorption. Annealing an H(ads)+D(ads) monolayer to 362 K for 90 s eliminates tLe isotope effect in the desorption results by allowing sufficient time to establish an equilibrium distribution of both isotopes in the subsurface sites. These data are consistent with photoemission and HREELS results on (111) facets of Ni, Pt, Pd, and Cu which also have suggested facile H-penetration into subsurface sites.