中文摘要：

运用Gaussian 03程序包中的单双迭代三重激发耦合簇理论和相关一致五重基优化了AsH2的基态结构，并在优化结构的基础上计算了它的离解能和振动频率．结果表明：AsH2基态的平衡构型具有C2v对称性，键长RAs-H=0．1508nm，键角么∠AsH=91．2231°，离解能De（HAs—H）=2．8795eV，振动频率v1（a1）=1013．3361 cm^-1，v2（a1）=2225．1347cm^-1，v3（a1）=2233．7565cm^-1．这些结果与实验值较为相符．对H2的基态使用优选出的CO—pV6Z基组、对AsH的基态使用优选出的cc—pV5Z基组进行平衡几何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Murrell—Sorbie函数．与实验数据及其他理论结果的比较表明，本文关于AsH（X^3∑^-）自由基光谱常数（D0，De，Re，ωe，Be，αe和ωeχe）的计算结果达到了很高的精度并最为完整．采用多体项展式理论导出了AsH2（C2v，X^2B1）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．首次报导了AsH2（C2v，X^2B1）自由基对称伸缩振动等值势能图中存在的两个对称鞍点，对应于反应AsH＋H→AsH2，势垒高度约0．1512×4．184kJ／mol．

英文摘要：

The CCSD（T） theory in combination with the cc-pV5Z basis set is used to determine the equilibrium geometry, dissociation energy and vibrational frequencies of AsH2 （ C2v, X^2 B1 ） radical. By comparison, excellent agreement can be found between the present results and the experiments. The values obtained at present are of 0. 1508 nm for the equilibrium bond length RAs-H , 91. 2231° for the bond angle ∠ HASH, 2. 8795 eV for the dissociation energy De （HAs-H） and 1013. 3361 cm^- 1,2225. 1347 cm^-1 and 2233.7565 cm^-1 for the vibrational frequencies v1 （ a1 ）, v2 （ a1 ） and v3 （ a1 ）, respectively. The equilibrium geometry,harmonic frequency and potential energy curve of the AsH（X^3∑^-） radical are calculated at the CCSD（T）/cc-pV5Z level of theory. The ab initio results are fitted to the Murrell-Sorbie function with the least-square method. The spectroscopic parameters are in excellent agreement with the experiments. The analytic potential energy function of the AsH2 （ C2v, X^2 B1 ） radical is derived by using the many-body expansion theory. This function correctly describes the configuration and dissociation energy of the AsH2 （C2v, X^2 B1 ） radical. Two symmetrical saddle points have been found at （0. 160 nm, 0.296 nm） and （0.296 nm,0. 160 nm） ,respectively. And the barrier height is equal to 0. 1512 ×4. 184 kJ/mol.