中文摘要：

使用Gaussian03程序包提供的CCSD（T）理论及Duning等的相关一致基cc-pVnZ和aug-cc-pVnZ（n=2,3,4,5）,对SD（X2Π）自由基的平衡核间距、谐振频率及相互作用势进行了计算,并拟合出了相应的光谱常数.在CCSD（T）/aug-cc-pV5Z理论水平下,光谱常数D0,De,Re,ωe,αe,B0及Be的值分别为3.65730eV,3.77669eV,0.13424cm-1,1938.372cm-1,0.09919cm-1,4.88585cm-1和4.8872cm-1,均与已有的实验结果相符很好.利用在CCSD（T）/aug-cc-pV5Z理论水平下获得的相互作用势,在绝热近似下通过数值求解双原子分子核运动的径向薛定谔方程,找到了J=0时SD（X2Π）自由基的全部23个振动态,完整地求出了每一振动态的振动能级及相应的经典转折点、惯性转动常数和离心畸变常数;在1.0×10-11—1.0×10-4a.u.的碰撞能区内通过数值求解原子-原子散射的径向薛定谔方程,研究了基态S原子和基态D原子沿SD（X2Π）相互作用势的弹性碰撞,计算了这一弹性碰撞的总截面和各分波截面,分析了各分波截面对总截面的影响.结果表明：总截面的形状主要由s分波截面决定,尽管直到l=4的各分波截面均有形状共振存在,但由于其强度都较弱,全部被湮没在较强的总弹性截面中.

英文摘要：

The equilibrium internuclear separations, harmonic frequencies and interaction potentials have been calculated by employing the CCSD（T） theory in combination with the series of the correlation- consistent basis sets, cc-pVnZ and aug-cc-pVnZ （n=2, 3, 4, 5）, of Dunning and co-workers. The potential energy curves are all fitted to the Murrell-Sorbie functions, which are used to determine the spectroscopic parameters. At the CCSD（T）/aug-cc-pV5Z level of theory, the values of D_0, D_e, R_e, ω_e, α_e, B_0 are 3.65730 eV, 3.77669 eV, 0.13424 cm-1, 1938.372 cm-1, 0.09919 cm-1, 4.88585 cm-1 and 4.8872 cm-1, respectively, which conform almost perfectly with the available measurements. With the analytic interaction potential obtained at the CCSD（T）/aug-cc-pV5Z level of theory, a total of 23 vibrational states has been predicted for the first time when the rotational quantum number J is set to equal zero （J =0） by solving the radial Schrdinger equation of nuclear motion. The complete vibrational levels, classical turning points, inertial rotation and centrifugal distortion constants are reproduced from the SD（X2Π） potential when J=0. The total and various partial-wave cross sections are calculated for the elastic collisions between the ground-state S and D atoms at energies from 1.0×10-11 to 1.0×10-4 a.u. when the two atoms approach each other along the SD（X2Π） interaction potential. No shape resonances can be found in the total elastic cross sections. The results show that the shape of the total elastic cross sections is mainly dominated by the s-partial wave at very low temperatures. Because of the weakness of the shape resonances coming from various partial waves, they are all covered up by the strong total elastic cross sections.