钚化合物分子结构、势能函数及分子反应动力学

【作者】 蒙大桥；

【导师】 朱正和；

【作者基本信息】 四川大学 ， 原子与分子物理， 2002， 博士

【摘要】 采用量子力学中密度泛函（DFT）B3LYP方法和相对论有效原子实模型（RECP），应用Gaussian98W程序，对钚化合物的分子结构，势能函数和Pu_n（n=2,3,4）分子结构稳定性进行了计算。并在得到势能函数的基础上对钚化合物反应动力学进行了研究，探讨了钚在水气中的氧化机理。 计算了PuO，PuH，PuH₂，HPuO，Pu₂，Pu₃和Pu₄的结构。在原子分子反应静力学基础上，根据分子电子状态构造的群论原理，确定了钚化合物分子的电子状态，分别为PuO（X⁷∑），PuH（X⁸∑），PuH₂（（?）⁷B₁），HPuO（（?）⁶A′₁）和它们对应的离解极限。 导出了PuO和PuH双原子分子的Murrell-Sorbie势能函数曲线，在此基础上推导出光谱项常数和力常数。利用多体项展式理论方法，导出PuH₂和HPuO三原子分子的解析势能函数，绘出其等值势能面图。等值势能面图正确地反映了其平衡构型及动力学特征。得到PuH₂和HPuO分子的三维分析势能函数。 在导出的势能函数基础上，采用准经典的Monte-Carlo轨线法研究了Pu+H₂和H+PuH的碰撞过程。根据反应截面与能量之间的关系，得到Pu+H₂→PuH₂（v=j=0）是无阈能反应。计算得到钚与氢气反应生成的主要产物是PuH₂。而反应H+PuH（v=j=0）生成PuH的阈能约为47.8kcal／mol，反应速度极慢。此外，碰撞结果还显示，Pu原子与H₂的反应在低能时，是显著的无阈能放热反应。能量较高时，反应截面急剧降低，当能量大于251.04kJ／mol时，则主要是非反应和完全离解的碰撞过程。这与在较高温度下PuH₂分解释放氢气的实验现象吻合。 Pu+HO，H+PuO和O+PuH的动力学研究结果表明：反应Pu+HO→PuO+H是显著的无阈能放热反应，生成产物基本是PuO+H。反应O+PuH→PuO+H同样是显著的无阈能反应。相反地，H+PuO则主要是非反应过程，即主要产物是H+PuO。还得到在有氢的情况下PuH与O的反应非常显著。这也与实 四川大学博士学位论文验得到有氢化物催化存在的情况下，金属钎与空气反应速率将大大提高的结论是和谐的。这为环在潮湿环境中的氧化腐蚀研究提供了理论依据，在理论与实践上得到结合点，具有重要意义。 首次发现PIV1习3，勺分子中的自旋极化效应。通过计算Pll、Pll卜Pll。和PU4，得到它们的自旋未配对电子分别为 6、12、18和 24个。即不存在自旋配对，所有价电子都处在不同的空间轨道上，这种自旋不平衡现象，称为自 二旋极化效应。平衡自旋电子的交换积分是正值，因此降低系统能量的效果，丁超过了自旋配对降低系统能量的效果。自旋极化效应在钢系元素以及重元素团簇中会比较突出。同时，用ah initio计算了Pny Pn。的力常数和离解能，成功导出了它们的势能函数解析表达式，作出了势能曲线等值图。 首次用 ah initio计算和群论对＊。对称性与稳定性作了系统的研究。从群的分解与直积导出了Jahn－Teller效应引起的分于几何构型变化后可能的电子态。优化了PU。的几何结构。结果发现至少有7个稳定的状态。群论分析结果与计算结果完全一致，发现h。分子中有明显的Jahn－Teller效应。更多还原

【Abstract】 Density functional Becke 3LYP method with relativistic effective core potential (RECP) and Gaussian 98W program have been used to investigate the structures and potential energy functions of plutonium compounds, and to investigate the geometrical configurations and stability of PuN(n=2,3,4) molecules. The atomic and molecular reaction dynamic processes for the reaction systems of plutonium compounds have been studied based on the present potential energy functions. The mechanism for the oxidation of metallic plutonium in moisture air has been discussed.Firstly, the possible electronic states and the reasonable dissociative limits for plutonium compounds have been derived based on the atomic and molecular reaction statics and the resolution of group representations. The molecular structures for PuO, PuH, PuH2, HPuO, Pu2, Pu3 and Pu4 have been optimized based on the Density functional Becke 3LYP method. Results show that the ground electronic states for PuO, PuH, PuH2 and HPuO are X7?, X8?, X7B1 and X6A respectively.However, the reaction rate for H+PuH(v-0,j=0) is far more lower comparing with that for Pu+H2(v=0,j=0). Secondly, the Murrell-Sorbie potential energy functions for the diatomic molecules PuO and PuH have been obtained according to the ab initio data through the least square fitting. The spectroscopic constants for PuO and PuH have been derived from the potential energy functions. The analytic potential energy functions for ground states of PuH2 and HPuO molecules have also been derived by many-boy expansion method using their equilibrium geometry structure parameters, dissociation energy and force constants of the tri-atomic molecules. Figures for the potential energy functions have bee given. These potential energy functions show the structure characteristics of the molecules exactly.Thirdly, the atomic and molecular reaction dynamic processes for the collisions system of Pu+H2 and H+PuH have been studied based on the present potential energy function of PuH2 by Monte-Carlo puasi-classical trajectory approach. It is can be concluded from the relationship between the initial energy and the reaction sections that Pu+H2(v=0,j=0) has no energy threshold, and the principal product of this reaction is PuH2. However, the energy threshold for H+PuH(v=0,j=0) is 47.8kcal.mol-1, and the reaction rate for H+PuH(v=0,j=0) is far more lower comparing with that for Pu+H^2(v=0,j=0)). The results also show that the reaction section for Pu+H2(v=0,j=0) decrease rapidly with the initial energy increasing. When the initial energy is over 251.04kJ.mol-1, the molecular reaction dynamic processes are mainly non-reaction. The results are good in agreement with the equilibrium pressure observed in the decomposition process of PuH2.The atomic and molecular reaction dynamic processes for the collisions systems of Pu+HO(v=0,j=0), H+PuO(v=0,j=0) and O+PuH(v=0,j=0) have also been studied. The results show that both Pu+HO and O+PuH have no energy threshold, and the principal products of these reactions are mainly PuO. However, H+PuO is a non-reaction process. The results also show that the reaction rate for PuH+O is very fast if PuHx exit in the reaction system. These conclusions are good in agreement with the experimental results observed in the investigation of metallic plutonium oxidation in air where small amount of PuHx exits. Our theoretical investigation results gives a reasonable explain for the experiment results. It is of great significance for the more understanding the oxidation corrosive mechanism of metallic plutonium in moisture air.The dissociation energy and harmonic force constants for Pu2 and Pu3 have been calculated for the first time. The potential energy functions for Pu2 and Pu3 have also been obtained.Then, we have found the spin-polarization effect in Pun(n=2,3,4) for the first time. The valence electrons of Pu are six. The non-pair electrons for Pu2, Pu3 and Pu4 are twelve, eighteen, and twenty-four respectively according to the present calculation. It is means that all of the valence el更多还原