BH2和AlH2分子的结构及其解析势能函数

运用二次组态相关(QCISD)方法，分别选用6-311++G(3df,3pd)和D95(3df,3pd)基组，对BH₂和AlH₂分子的结构进行了优化计算，得到BH₂分子的稳态结构为C_2v构型，电子态为²A₁、平衡核间距R_BH=0.1187nm、键角∠HBH=128.791°、离解能D_e=3.65eV、基态振动频率ν₁(a₁)=1020.103cm^-1,ν₂(a₁)=2598.144cm^-1,ν₃(b₂)=2759.304cm^-1.AlH₂分子的稳态结构也为C_2v构型，电子态为²A₁、平衡核间距R_AlH=0.1592nm、键角∠HAlH=118.095°、离解能D_e=2.27eV、基态振动频率ν₁(a₁)=780.81cm^-1,ν₂(a₁)=1880.81cm^-1，ν₃(b₂)=1910.46cm^-1.采用多体项展式理论推导了基态BH₂和AlH₂分子的解析势能函数，其等值势能图准确再现了BH₂和AlH₂分子的结构特征及其势阱深度与位置.分析讨论势能面的静态特征时得到BH+H→BH₂反应中存在鞍点，活化能为150.204kJ/mol；AlH+H→AlH₂反应中也存在鞍点，活化能为54.8064kJ/mol.关键词：2')" href="#">BH₂2')" href="#">AlH₂Murrell-Sorbie函数多体项展式理论解析势能函数

Structure and analytic potential energy functions of the molecules BH2 and AlH2

Quadratic configuration interaction (QCISD) method has been used to optimize the possible ground-state structures of BH₂ and AlH₂ molecules. The results show that the ground state of BH₂ molecule has C_2v symmetry and is in the ²A₁ state. The parameters of structure and the harmonic frequencies are R_BH=0.1187nm, ∠HBH=128.7914°, D_e=3.65eV,ν₁(a₁)=1020.103cm^-1,ν₂(a₁)=2598.144cm^-1 and ν₃(b₂)=2759.304cm^-1, respectively. The results also show that the ground state of AlH₂ molecule has C_2v symmetry and is in the ²A₁ state. The parameters of structure and the harmonic frequencies are of R_AlH=0.1592nm, ∠HAlH=118.095°, D_e=2.27eV,ν₁(a₁)=780.81cm^-1,ν₂(a₁)=1880.81cm^-1 and ν₃(b₂)=1910.46cm^-1, respectively. The potential energy functions of BH₂ and AlH₂ have been derived from the many-body expansion theory. The potential energy functions describe correctly the configurations and the dissociation energies of the two ground-state molecules. Molecular reaction kinetics of BH+H and AlH+H based on the potential energy functions is discussed briefly.