A molecular-beam investigation of the scattering,adsorption and absorption of H2 and D2 from/on/in Pd(111)

H₂ and D₂ are scattered from clean Pd(111) and a saturated chemisorption layer in a highly specular distribution. Evidence for an ordering of the adiayer with increasing coverage is seen. The hydrogen-deuterium exchange occurs via a Langmuir-Hinshelwood mechanism, and the temperature dependence of the rate of HD production can be understood without assuming an activation energy for equilibration. Lock-in and wave-form analyses of scattered H₂ + D₂ mixed beams show that equilibrium between adsorbed hydrogen and deuterium and that dissolved just below the surface is reached rapidly at temperatures above 300 K.