UNUSUAL BEHAVIOR OF CHEMICAL WAVES IN THE NO-2 REACTION ON RH(111) - LONG-RANGE DIFFUSION AND FORMATION OF PATCHES WITH REDUCED WORK FUNCTION(H)

Pattern formation in the NO + H-2 reaction on Rh(111) has been investi gated in the 10(-6) mbar range using photoelectron emission microscopy (PEEM) as a spatially resolving method Target patterns, spiral waves and irregular patterns are observed in a T-window of similar to 20 K w idth at around 460 K, located in the transition range between the reac tive and unreactive states of the surface. A new species characterized by a work function below that of the clean surface forms upon collisi on of two wave fronts. This new species is tentatively assigned to sub surface oxygen. The colliding wave fronts start to interact when they are still more than 100 mu m apart, thus demonstrating the presence of a long-range diffusional coupling.