Coadsorption of NO and D 2 on Rh(100)

Abstract

The coadsorption of NO and D 2 on Rh(100) at 100 K has been studied using thermal desorption spectroscopy, low energy electron diffraction and work-function-change measurements. During thermal desorption a small amount of water is detected and arguments are presented for its formation from adsorbed D(a) and O(a), the latter being formed by dissociation of NO. The dissociation of NO to form N 2 and O 2 is not altered measurably by the presence of D(a). There is competition for sites in the adsorption of D 2 and molecular NO. While NO can partially displace the preadsorbed D 2, dosing D 2 does not alter the concentration of preadsorbed NO. At 100 K, when the surface is saturated with NO ( θ sat=0.65 ML), the adsorption of D 2 is completely inhibited. However, when the surface is saturated with D(a) ( θ sat=1 ML), an appreciable amount of NO (∼0.5 ML) can still be adsorbed. The NO, N 2 and O 2 desorption kinetics are unchanged when D(a) is added, but D 2 TDS is modified due to interactions with NO-derived adspecies. The low temperature D 2 desorption peak shifts to higher temperature and increases in intensity with increasing NO coverage. Work-function changes are discussed in terms of mixing, as opposed to segregation, of the coadsorbed species.