Ab Initio Molecular Dynamics Study of the Reaction of U+ and U2+ with H2O in the Gas Phase: Direct Classical Trajectory Calculations

The gas phase reactions of U+ and U2+ with H2O were investigated using an ab initio molecular dynamics method. All of the information along the minimum energy path were calculated with density functional theory (DFT) and coupled cluster methods. For U+ with H2O, the molecular dynamics simulations yield a branching ratio of 86% for the H2 elimination channel to 14% for the H atomic elimination channel in agreement with the quadruple ion trap mass spectrometry (QIT/MS) experimental ratio of 91% to 9%. In the case of U2+ + H2O, there is a crossing of the potential energy surfaces (PES) after the first transition state. Crossing seams between the PES and possible spin inversion processes were studied by means of the intrinsic reaction coordinate (IRC) approach. For U2+ with H2O, all trajectories are corresponds to H atom elimination channel, this is consistent with the Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) experimental results. The chemical bonding evolution along the reaction pathways was discussed by using topological methodologies of the electron localization function (ELF).本研究采用从头算分子动力学(ab initio molecular dynamics)方法，系统探究了一价铀离子(U⁺)与二价铀离子(U²⁺)分别与水分子(H₂O)的气相反应行为。所有最低能量路径上的相关信息均通过密度泛函理论(DFT)与耦合簇方法完成计算。针对U⁺与H₂O的反应，分子动力学模拟结果显示，氢分子消除通道与氢原子消除通道的分支比为86%:14%，与四极离子阱质谱(QIT/MS)测得的91%:9%实验比值一致。对于U²⁺与H₂O的反应体系，其首个过渡态后出现势能面(PES)交叉现象。本研究借助内禀反应坐标(IRC)方法，对势能面间的交叉缝及潜在的自旋反转过程进行了分析研究。U²⁺与H₂O的所有反应轨迹均对应氢原子消除通道，该结果与傅里叶变换离子回旋共振质谱(FTICR-MS)的实验数据相符。本研究还通过电子定域化函数(ELF)的拓扑分析方法，探讨了各反应路径沿线的化学键演化规律。