Among fundamental diatomic molecules, the adsorption of carbon monoxide (CO) and nitric oxide (NO) on metal surfaces has been a subject of intensive research in the surface science community, partly owing to its relevance to heterogeneous catalysis used for environmental control. Compared to the rather well-defined adsorption mechanism of CO, that of NO is less understood because the adsorption results in much more complex reactions. The complexity is ascribed to the open-shell structure of valence electrons, making the molecule readily interact with the metal surface itself as well as with co-adsorbed molecules. Furthermore, the interaction crucially depends on the local structure of the surface. Therefore, to elucidate the interaction at the molecular scale, it is essential to study the valence state as well as the bonding geometry for individual NO molecules placed in a well-defined environment on the surface. Scanning tunneling microscopy (STM) is suitable for this purpose. In this review, we summarize the knowledge about the interaction of NO with metal surfaces, mainly focused on the valence electronic states, followed by recent studies using STM and atomic force microscopy (AFM) at the level of individual molecules.

在基本的双原子分子中，一氧化碳（CO）和一氧化氮（NO）在金属表面上的吸附已成为表面科学界广泛研究的课题，部分原因是其与用于环境控制的非均相催化作用相关。与相当明确定义的CO吸附机理相比，对NO的吸附机理知之甚少，因为吸附会导致更为复杂的反应。复杂性归因于价电子的开壳结构，使分子易于与金属表面本身以及与共吸附分子相互作用。此外，相互作用主要取决于表面的局部结构。因此，为了阐明分子水平上的相互作用，必须研究放置在表面上明确定义的环境中的单个NO分子的化合价态以及键的几何形状。扫描隧道显微镜（STM）适用于此目的。在这篇综述中，我们总结了关于NO与金属表面相互作用的知识，主要集中在价电子态，随后是最近在单个分子水平上使用STM和原子力显微镜（AFM）进行的研究。