Understanding heterogeneous catalysis at the atomic level requires detailed knowledge of the reactivity of different surface sites toward specific bond breaking and bond making events. We illustrate a new method in such investigations. We use a macroscopically curved Pt single crystal containing a large variation in density of highly kinked steps of two different chiralities. Scanning tunneling microscopy maps the entire range of surface structures present on the 31° section surrounding the Pt(111) apex. Whereas most of the surface shows the expected characteristic arrays of parallel steps, hexagonally-shaped, single-atom deep pits remain after cleaning procedures near the apex. Their orientation is indicative of the different chiralities present on the two sides of the crystal’s apex. These unintended defects locally raise the surface defect concentration, but are of little consequence to subsequent reactivity measurements for \(\text {D}_2\) dissociation and H–D exchange as probed by supersonic molecular beam techniques. We quantify absolute elementary dissociation and relative isotopic exchange rates across the surface with high spatial resolution. At low incident energies, elementary dissociation of the homonuclear isotoplogues is dominated by the kinked steps. H–D exchange kinetics depend also mostly linearly on step density. The changing ratio of D₂ dissociation to H–D formation, however, suggests that anisotropic diffusion of H(D) atoms is of influence to the measured HD production rate.

要了解原子级的多相催化作用，需要详细了解不同表面位点对特定键断裂和键形成事件的反应性。我们在此类调查中说明了一种新方法。我们使用宏观弯曲的Pt单晶，其中包含两种不同手性的高度扭结阶跃的密度变化很大。扫描隧道显微镜可绘制出Pt（111）顶点周围31°截面上存在的整个表面结构范围。尽管大多数表面显示了预期的平行台阶特征阵列，但在顶点附近进行清洁程序后仍保留了六边形的单原子深凹坑。它们的取向表明晶体顶点两侧存在不同的手性。\（\ text {D} _2 \）离解和H–D交换，由超音速分子束技术探测。我们以高空间分辨率量化整个表面的绝对基本解离和相对同位素交换率。在低入射能量下，同核同位素同质子的基本解离以扭结台阶为主。H-D交换动力学也主要取决于步长密度。然而，D _2的解离与H–D形成的变化比率表明，H（D）原子的各向异性扩散会影响所测量的HD生产率。