H/D-isotope effects in chemical wave propagation on surfaces:: the O2+H2 and NO+H2 reactions on Rh(110) and Rh(111)

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. (C) 1999 Elsevier Science B.V. All rights reserved.