低温下含氮的原子与自由基反应的量子动力学研究

Nitrogen-bearing atom-radical reactions at low temperatures play important roles not only in many important processes such as the formation mechanism of N2 in the cold interstellar clouds, but also in combustion process and atmospheric chemistry. Accurate rate constants of these radical-radical reactions at low temperatures are essential for astrochemical models, but it is still difficult to measure these rate constants experimentally. Atom-radical reactions are barrierless and highly exothermic and involve at least one complex along the reaction path. It is still a challenging for accurate quantum dynamics of such reactions. In this proposal, we will combine the state-of-the-art quantum chemistry computational method with quantum dynamic calculations to construct highly accurate ground and excited potential energy surfaces including non-adiabatic couplings for several nitrogen-bearing small molecular systems, such as NOH, NCH, and N2H. We will improve the quantum wave packet calculation method at low temperatures and increase the computational efficiency and accuracy. In addition, we will investigate the reactivity and state-to-state dynamics of the related atom-radical reactions at low temperatures with closely collaboration with the experimental studies to reveal the nature of these reactions. Our studies will provide new platforms for further experimental and theoretical studies. The proposed research will greatly improve our understanding of detailed microscopic mechanism of atom-radical reactions in low temperatures and play important roles in the protection of human living environment.

低温下含氮的原子与自由基反应不仅与星际云层中的重要过程(如氮气的形成)密切相关，而且在燃烧过程和大气化学中也具有重要的作用。低温下自由基之间的精确的反应速率常数是天体化学模型中的关键参数，但实验上仍难以探测。原子与自由基的反应由于反应路径中没有能垒，至少有一个中间复合物形成，且都是放热反应，这也给动力学研究带来了困难。在本项目中，我们将结合最先进的量子化学计算方法和量子动力学计算，构建高精度的含氮的小分子体系如NOH、NCH和N2H等的电子基态和激发态的势能面及其非绝热耦合；改进低温下量子波包的计算方法，提高计算效率和精度；研究在低温条件下相关的原子与自由基反应的反应活性及态－态动力学性质，与实验研究紧密结合，揭示低温环境下原子与自由基反应的本质，为进一步的实验和理论研究提供理论依据。本项目的研究对深入了解和认识原子与自由基在低温时的反应的细致的微观机制和人类生存环境的保护等具有重要意义。

本项目主要开展含氮的原子与自由基反应及小分子的态-态光解动力学的理论研究，取得了系列重要的研究进展。利用高级别量子化学从头算方法和大基组发展了NOH、NC2、HCN和N2H等含氮的小分子体系的高精度的电子基态和激发态的势能面，结合实波包传播方法研究了在低温条件下相关的原子与自由基反应的反应活性及态－态动力学性质，如定量预测了N+OH、N+CH和N+C2等反应的低温速率常数，且与最新实验结果十分吻合，揭示了一些低温环境下原子与自由基反应的本质，为进一步的实验和理论研究提供理论依据。研究了氨和苯酚等分子的光解动力学性质，发现在氨分子的光解过程中不能通过初态振转模式的选择来调控产物电子态分支比，计算的苯酚分子第一电子激发态振动基态的寿命与实验值十分吻合，并发现常用的绝热模型对描述锥形交叉附近的动力学过程是不正确的。在国际重要学术期刊上发表论文21篇，多次受邀在国际学术会议做报告。培养了1名博士后和5名博士。