We can also develop a different picture for non-equilibirum hydriding at millibar H 2 pressures by comparing our adsorption energy studies to previously published values of H 2 molecular adsorption and dissociation and H ion subsurface penetration on the (100) and (111) surfaces. Published data of this type is not available for the (110) surface and hence we limit our discussion to these two surfaces. On (100), an adsorbed H 2 molecule is held to the surface only weakly, 0.15 eV (6 k B T ). Computed dissociation energy barriers vary, 0.22 eV (9 k B T ) 6 to 0.49 eV (19 k B T ) to 0.78 eV (30 k B T ), but are all higher than the desorption barrier, suggesting that hydrogen molecules desorb and re-adsorb many times before dissociating. Once dissociated, the barrier to recombine is 1.44 eV (56 k B T ), while the energy barrier for a surface hydrogen atom to burrow into a subsurface T site is 0.93 eV (36 k B T ). Comparing the barriers for burrowing and recombination suggests, in turn, that surface hydrogen atoms are more likely to move into the bulk than recombine into an H 2 molecule.