Adsorption and Absorption Energies of Hydrogen with Palladium

Thermal recombinative desorption rates of HD on Pd(111) and Pd(332) are reported from transient kinetic experiments performed between 523 and 1023 K. A detailed kinetic model accurately describes the competition between recombination of surface-adsorbed hydrogen and deuterium atoms and their diffusion into the bulk. By fitting the model to observed rates, we derive the dissociative adsorption energies (E _{0, ads} ^H₂ = 0.98 eV; E _{0, ads} ^D₂ = 1.00 eV; E _{0, ads} ^HD = 0.99 eV) as well as the classical dissociative binding energy ϵ_ads = 1.02 ± 0.03 eV, which provides a benchmark for electronic structure theory. In a similar way, we obtain the classical energy required to move an H or D atom from the surface to the bulk (ϵ_sb = 0.46 ± 0.01 eV) and the isotope specific energies, E _{0, sb} ^H = 0.41 eV and E _{0, sb} ^D = 0.43 eV. Detailed insights into the process of transient bulk diffusion are obtained from kinetic Monte Carlo simulations.