H/D-isotope effects in chemical wave propagation on surfaces: the O 2+H 2 and NO+H 2 reactions on Rh(110) and Rh(111)

Abstract

H/D-isotope effects in chemical wave propagation in the bistable O 2+H 2 reaction on Rh(110) and Rh(111) and in the excitable NO+H 2 reaction on Rh(110) were investigated using photoemission electron microscopy (PEEM) as spatially resolving method. The systems were studied in the 10 −6–10 −4 mbar range between 400 K and 700 K. For equivalent partial pressures, i.e., partial pressures which have been corrected for the different impingement rates of H 2 and D 2, front and pulse propagation with H 2 is typically faster than with D 2 up to a factor of three. A similar difference exists with respect to the width of the existence range for pattern formation in pH 2(D 2), which is broader with D 2 than with H 2. Titration experiments of the oxygen-covered Rh(110) surface demonstrated that at high oxygen coverages, the reactive sticking of D 2 is inhibited much more strongly than with H 2. From the T-dependence of the front velocities, apparent activation energies were determined for the two isotopes.