The cyanonitrene radical, NCN, has been shown in the last two decades to play a crucial role in the formation of prompt-NO in combustion. This has stimulated a large number of experimental and theoretical studies on fundamental physico-chemical properties of NCN as well as on mechanistic and kinetic aspects of NCN reactions under combustion conditions. In this review, spectroscopic, thermodynamic, and kinetic data of NCN are collected and discussed. Methodic approaches for the detection of NCN in flames and in kinetic experiments are elucidated, and the suitability of cyanogen azide, NCN₃, as a precursor for NCN in kinetic experiments is examined. Kinetic and mechanistic aspects of a number of NCN elementary chemical steps are extensively reviewed. Regarding prompt-NO formation, the role of the reaction network initialized by the reaction CH + N₂ ⇌ NCN + H is examined by modeling measured flame profiles of NCN, HCN, and NO. In these simulations, the critical role of the product channel-branching of the NCN + H reaction, termed the prompt-NO switch, is confirmed. A particularly sensitive balance is observed between the product channels leading back to CH + N₂ or forward to HCN + N. The roles of spin conservation and intersystem crossing processes under flame conditions and in kinetic experiments with NCN₃ as NCN precursor are highlighted. A number of critical points and remaining open problems in NCN chemistry and prompt-NO formation are indicated.

在过去的 20 年中，氰腈自由基 NCN 已被证明在燃烧中形成瞬态一氧化氮中起着至关重要的作用。这激发了大量关于 NCN 基本理化性质以及 NCN 反应在燃烧条件下的机械和动力学方面的实验和理论研究。在这篇综述中，收集和讨论了 NCN 的光谱、热力学和动力学数据。阐明了在火焰和动力学实验中检测 NCN 的系统方法，以及叠氮化氰 NCN ₃的适用性，作为 NCN 在动力学实验中的前体进行了检查。许多 NCN 基本化学步骤的动力学和机械方面进行了广泛的审查。关于瞬发 NO 的形成，通过对 NCN、HCN 和 NO 的测量火焰剖面建模，研究了由反应 CH + N ₂ ⇌ NCN + H初始化的反应网络的作用。在这些模拟中，确认了 NCN + H 反应的产物通道分支的关键作用，称为提示-NO 开关。在返回 CH + N ₂或前进至 HCN + N的产物通道之间观察到特别敏感的平衡。 自旋守恒和系统间交叉过程在火焰条件下和 NCN ₃动力学实验中的作用作为 NCN 前体被突出显示。指出了 NCN 化学和快速 NO 形成中的许多关键点和尚待解决的问题。