Square chemical waves in the catalytic reaction NO + H2 on a rhodium(110) surface
Square chemical waves in the catalytic reaction NO + H2 on a rhodium(110) surface
复制标题
铑(110)表面催化反应NO H2中的方形化学波
作者：
F. Mertens;R. Imbihl
早在19061年，人们就认识到，自催化反应和自催化组分扩散之间的耦合可以产生一个传播的反应前沿--化学波。化学波已被深入研究，在流体相反应扩散systems 2，但在最近几年的各种时空模式也被观察到的振荡反应在单晶surfes 3，4。一个重要的新的方面，已介绍了这些研究是各向异性扩散，作为固定的表面几何形状上发生的吸附颗粒的扩散的结果。在这里，我们报告的过渡观察从椭圆形的正方形同心化学波在铑（HO）表面上的NO和H2的反应。椭圆形图案的特点是简单的各向异性扩散，但我们属性的起源的正方形图案的状态依赖的各向异性，即各向异性变化沿着波剖面的吸附覆盖的变化产生不同的重建的基板结构。扩散各向异性和系统状态之间的这种相互作用可以预期是相当普遍的，并产生新的振荡图案。
IT WAS realized as early as 19061 that coupling between an autocatalytic reaction and the diffusion of the autocatalytic component can give rise to a propagating reaction front—a chemical wave. Chemical waves have been studied intensively in fluid-phase reaction–diffusion systems2, but in recent years a variety of spatiotemporal patterns has also been observed for oscillatory reactions on single-crystal surfaces3,4. One important new aspect that has been introduced by these studies is that of anisotropic diffusion, as a consequence of the fixed surface geometry on which the diffusion of the adsorbed particles takes place. Here we report the observation of a transition from elliptical to square-shaped concentric chemical waves in the reaction of NO and H2 on a rhodium(HO) surface. The elliptical pattern is characteristic of simple anisotropic diffusion, but we attribute the origin of the square pattern to a state-dependent anisotropy—that is an anisotropy that varies along the wave profile as changes in the adsorbate coverage generate different reconstructions of the substrate structure. This interplay between diffusional anisotropy and the state of the system can be expected to be quite general and to give rise to new varieties of oscillatory patterning.