Isotope effect in the surface diffusion of hydrogen and deuterium on Ru(001)

The surface diffusion of hydrogen and deuterium on Ru(001) at low coverage was studied using laser-induced thermal desorption techniques. In the temperature range from 260 to 300 K, the surface diffusion coefficients could be expressed in Arrhenius form as DH=6.9×10−4 cm2/s exp(−3.6±0.5 kcal mol−1/RT) and DD=4.6×10−4 cm2/s exp(−4.1±0.5 kcal mol−1/RT) for hydrogen and deuterium, respectively. The observed isotope effect was somewhat larger than predicted by simple transition state theory but was within the limits of experimental error. Quantum mechanical tunneling can be playing, at best, only a minor role in the surface migration of hydrogen on Ru(001) at these temperatures.