School of Chemistry, University of Nottingham, University Park, NG7 2RD, UK.
Phys Chem Chem Phys. 2018 Oct 17;20(40):25931-25938. doi: 10.1039/c8cp05681a.
The protonated water clusters present in the D-region of the ionosphere have been postulated to be formed from cluster ions such as O2+·(H2O)n and NO+·(H2O)n, although the detailed mechanism of the underlying reactions is not understood. Second order Møller-Plesset perturbation theory based Born-Oppenheimer ab initio molecular dynamics (AIMD) simulations of the reactions of the O2+·(H2O)n and NO+·(H2O)n cluster ions to form protonated water clusters reveal different mechanisms for the O2+ and NO+ based ions. AIMD simulations of O2+·(H2O)n=2-5 with initial velocities of the atoms sampled from the Maxwell-Boltzmann distribution at 220 K show that following charge transfer, a reaction to form a protonated water cluster and OH occurs rapidly where the neutral O2 molecule is just a spectator. In contrast, the reaction of NO+·(H2O)n=4,5 has been hypothesised to involve an intracluster reaction, but no reaction is observed in AIMD simulations using thermal initial velocities. However, it is shown that reactions to form protonated water clusters do occur in simulations when a water molecule collides with a NO+·(H2O)4 cluster.
在电离层 D 区中存在的质子化水分子簇被认为是由诸如 O2+·(H2O)n 和 NO+·(H2O)n 等簇离子形成的，尽管底层反应的详细机制尚不清楚。基于二阶 Møller-Plesset 微扰理论的 Born-Oppenheimer 从头算分子动力学（AIMD）模拟研究了 O2+·(H2O)n 和 NO+·(H2O)n 簇离子的反应，以形成质子化水分子簇，揭示了基于 O2+ 和 NO+ 的离子的不同反应机制。在 220 K 下从麦克斯韦-玻尔兹曼分布中采样原子初始速度的 O2+·(H2O)n=2-5 的 AIMD 模拟表明，在电荷转移后，迅速发生形成质子化水分子簇和 OH 的反应，其中中性 O2 分子只是旁观者。相比之下，已经假设 NO+·(H2O)n=4,5 的反应涉及到内簇反应，但在使用热初始速度的 AIMD 模拟中未观察到反应。然而，当水分子与 NO+·(H2O)4 簇碰撞时，在模拟中确实发生了形成质子化水分子簇的反应。
