非Born—Oppenheimer近似理论下水分子H2O（X^1A1）的结构与分析势能函数

基于群论理论和原子分子反应静力学正确判断了H2O（X^1A1）离解极限。采用密度泛函B31yp／6-311＋＋g^＊＊方法优化出H2O（X^1A1）了平衡几何、离解能和振动频率．考虑核振动能量，修正Bom—Oppenheimer近似理论下的分子势能函数，计算了H2O（X^1A1）分子的二阶力常数、正则振动频率和零点能。使用多体项展式理论方法导出了基态H2O（X^1A1）分子非Bom—Oppenheimer近似理论下的分析势能函数，然后根据该修正势能函数绘出等值势能图，并讨论了H＋OH反应和O＋H2反应的势能面静态特征。结果表明：在H＋OH—H2O通道上反应为无阈能反应，而O＋HH→H2O存在鞍点，反应具有一定的方向性，以垂直H—H键的方向最为有利。

Analytical potential energy function for the ground state H2O((X)1A1) of H20 under non-born-oppenheimer approximation

Based on group theory and atomic and molecular reactive statics （AMRS）, the reasonable dissociation limits of H2O are determined. The present work devote to deriving the modified potential energy function of H2O（X^1A1） under non-Born-Oppenheimer approximation using many body expansion method, which need to consider its nuclear vibration energy. The equilibrium geometry, dissociation energy and vibration frequency of H2O（X^1A1） are calculated by using the density-functional theory （DFT） B31yp.The force constants and zero point energy from this modified potential energy function of H2O（X^1A1） all are fair reasonable. The potential contours have been drawn from this potential energy function of H2O（X^1A1）, it shows that the reactive channel H＋OH→H2O is non-threshold energy for its radical reaction, and the channel O＋HH→H2O presents saddles, which indicates that the radical reaction has certain direction, and the direction which vertical the H-H bond is the most satisfied.