Spatial distribution of N2 and NO desorbing from a Rh(533) surface

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Abstract
The spatial distribution of N2 and NO desorbing from Rh(533), Rh(S)-[4(111)×(100)], was measured along the [65̄ 5̄] direction (along the steps) after adsorption of NO at 320 K. The N2 desorption at 450 K and 600 K showed a specific spatial distribution, that is, there was no peak either normal to the (111) terraces (θ=+14.4°) or normal to the (100) steps (θ=−40.3°), but a desorption maximum around θ=−15°. Integrated TPD spectra of N2 from the NO preadsorbed Rh(533) surface were very similar to those on Rh(111), but the spatial distribution of N2 from Rh(533) indicates desorption of N2 from the boundary between the (111) terraces and the vacant (100) steps. The spatial distribution of NO desorbing from the Rh(533) surface at 420 K obeyed cos θ, indicative of desorption normal to the crystal surface. Contrary to this, the spatial distribution of the desorption of NO molecules produced by the recombination reaction of adsorbed N and O desorbed at 550 K exhibits a peak intensity at θ=+15° (normal to the (111) terraces).