(179f) Measurements of Structure Sensitivity Spanning Surface Orientation Space

We have used spherically curved Cu(hkl) single crystals to make measurements of surface reaction kinetics on 169 different surface orientations vicinal (within 12^o) to Cu(111). The experiments started with a uniform monolayer of tartaric acid (TA) on the surface at 433 K, followed by spatiotemporally resolved x-ray photoemission spectroscopy measurements of coverage θ[t, (hkl)] as the TA decomposed at each point on the surface. The data at each surface orientation were analyzed using the predetermined rate law for TA decomposition on Cu surfaces. These have yielded the rate constants, k(hkl) for the decomposition of D- and L-tartaric (TA), meso-tartaric and D- and L-aspartic acid (Asp) as continuous functions of surface orientation, (hkl). The kinetics exhibit structure sensitivity and enantiosensitivity (for those surface orientations and adsorbates that are chiral). This has yielded the highest resolution maps of surface reactivity versus crystallographic orientation yet obtained. The Figure shows polar angle plots of the inverse half-lives, 1/t_1/2, of D- and L-TA decomposition at T = 433 K measured as functions of surface orientation relative to the Cu(111) direction. The Cu(111) surface at the center point is the least reactive (blue). As the step density increases towards the edges of the crystal, the activity for TA decomposition increases (red), but not isotropically. What is most interesting is that the decomposition of D- and L-TA reveals clear enantiospecificity. The activity for D-TA decomposition is clearly highest in the region of the surface exposing S-kinks, and vice versa for the decomposition of L-TA.