A BOUNDARY FOR REACTION-MECHANISMS WITHIN THE TRANSITION-METALS INTERACTING WITH NITROGEN-OXIDES IS OBSERVED IN DSIMS EXPERIMENTS

Dynamic secondary ion mass spectrometry (DSIMS) investigations have be en carried out with Cr, Mn, Fe, Co, Mo, Rh, W, Re, Os and Ir under 4 m Pa N2O, NO and 3 mPa NO2 as reactant gases. Results indicate similar b ehaviour in adsorption for Cr, Mn, Fe, Mo, W on the one hand and for C o, Rh, Os and Ir on the other. For the first group of metals the nitro gen oxide molecules are always totally destroyed in adsorption whereas the second group shows evidence for surface compounds such as MeNO (M e = metal) indicating only a partial dissociation in the case of N2O a nd NO2, and molecular adsorption under NO respectively. Re does not be long uniquely to either group because it reacts with N2O and NO2 disso ciatively whereas under NO only partial dissociation is observed.