中文摘要：

运用单双迭代三重激发耦合簇理论和相关一致五重基对SiH2的基态结构进行了优化，并在优化结构的基础上进行了离解能和振动频率的计算．结果表明：SiH2的基态为C2结构，平衡核间距RSi-H=0．15163nm，H—Si—H键的键角α=92．363°，离解能De（HSi-H）=3．2735eV，频率v1（a1）=1020．0095cm^-1，v2（a1）=2074．8742cm^-1，v3（a1）=2076．4762cm-1．这些结果与实验值均较为相符．对H2的基态使用优选出的CC—pV6Z基组、对SiH的基态使用优选出的aug-cc-pV5Z基组进行几何构型与谐振频率的计算并进行单点能扫描，且将扫描结果拟合成了解析的Murrell-Sorbie函数．与实验结果及其他理论计算结果的比较表明，本文关于SiH自由基光谱常数（Dc，Re，ωe，Be，ae和ωexx）的计算结果达到了很高的精度．采用多体项展式理论导出了SiH2（C2r，X1A1）自由基的解析势能函数，其等值势能图准确再现了它的离解能和平衡结构特征．同时还给出了SiH2（C2v，X1A1）自由基对称伸缩振动等值势能图中存在的两个对称鞍点，对应于SiH＋H→SiH2反应，势垒高度为0．5084eV．

英文摘要：

The coupled-cluster single-double withy a perturbative triple excitations [CCSD（T）] theory in combination with the quintuple correlation-consistent basis set （cc-pV5Z） of Dunning and co-workers is employed to determine the equilibrium geometry, dissociation energy and vibrational frequencies of the Sill2 （ C2ν, X1 AI ） radical. By comparison, excellent agreement can be found between the present results and the experiments. The values obtained at cc-pV5Z are 0. 15163 nm for the equilibrium bond length RSi-H, 92.363° for the bond angle a of H--Si-H, 3.2735 eV for the dissociation energy De（HSi-- H） and 1020.0095, 2074.8742 and 2076.4762 cm-l for the vibrational frequencies ν1 （ a1 ）,ν2 （ al ） and ν3 （ a1 ）, respectively. The equilibrium geometry, harmonic frequency and potential energy curve of the Sill（X2Ⅱ） radical are calculated at the CCSD（T）/aug-cc-pV5Z level of theory. The ab initio points are fitted to the Murrell-Sorbie function with the least-squares method. The spectroscopic parameters, whether directly determined by the Gaussian03 program package or they are derived from the analytic potential energy function, conform almost perfectly with the available experimental results. The analytic potential energy function of the SiH2（ C2v, X1 A1） radical is derived by using the many-body expansion theory. This function correctly describes the configuration and dissociation energy of the SiH2 （C2v, X1 A1 ） radical. Two symmetrical saddle points have been found at （0.312, 0. 160 nm） and （0. 160, 0.312 nm）, respectively. And the barrier height is found to be 0.5084 eV.