New reactions of diazene and related species for modelling combustion of amine fuels

Potential energy surfaces for reactions involving N2H2 isomers of diazene (diimide) have been explored using density functional theory, with energies based on coupled-cluster theory. A focus is on processes that create or consume these species, and isomerisation between the E (trans) and Z (cis) forms of HNNH. These include isomerisation and dissociation pathways for HNNH, addition of H atoms to form N2H3, abstraction by H atoms yielding short-lived NNH, and abstraction reactions of H with N2H3. Transition state and capture theories are applied for high-pressure-limiting behaviour, while low-pressure and falloff regions are characterised via the methods of Troe and coworkers. Rate constants and thermochemistry are provided to improve models of diamine chemistry, relevant to the combustion of NH3 especially at high concentrations, high pressures or under reducing conditions. Results indicate that amine radical recombination mainly yields the E HNNH isomer, while H-abstraction from N2H3 results in E HNNH and H2NN. However, at elevated temperature E → Z isomerisation becomes competitive, and Z HNNH, being more reactive, acts to enhance the diazene consumption rate.

本研究采用密度泛函理论（density functional theory）探究了涉及二亚胺（diazene，又称diimide）的N₂H₂异构体的反应势能面，能量计算基于耦合簇理论（coupled-cluster theory）。研究重点聚焦于生成或消耗此类物种的反应过程，以及HNNH的E型（反式，trans）与Z型（顺式，cis）之间的异构化反应。此类反应路径包括HNNH的异构化与解离路径、氢原子加成生成N₂H₃的反应、氢原子抽提生成短寿命NNH的反应，以及H与N₂H₃之间的抽提反应。针对高压极限下的反应行为，本研究采用过渡态理论（transition state theory）与捕获理论（capture theory）进行分析；而低压区及跌落区域的反应特征，则通过Troe及其同事提出的方法进行表征。本数据集提供了速率常数与热化学数据，以优化二胺化学的反应模型，该模型与氨（NH₃）的燃烧过程密切相关，尤其适用于高浓度、高压或还原气氛下的燃烧场景。研究结果表明，胺自由基的复合反应主要生成E型HNNH异构体；而从N₂H₃中抽提氢原子的反应则会生成E型HNNH与H₂NN。然而，当温度升高时，E型向Z型的异构化反应会成为竞争性路径；由于Z型HNNH具有更高的反应活性，其会加速二亚胺的消耗速率。