中文摘要：

通过系统的使用完全活化空间自洽场（CASSCF）和多组态二阶微扰理论（CASPT2）方法结合ANORCC（TZP）基组研究了CH3Se自由基的低能电子态相关性质,计算过程中,采用Cs对称性.实验结果表明,该自由基的Jahn-Teller效应不明显（69 cm^（-1））,基态电子态1^2A＇与其简并态1^2A″形成8 cm^（-1）的微小劈裂,这一点与实验值形成较好的吻合.计算所得基态电子态的C—Se的拉伸频率ν6（a＇）为554.1 cm^（-1）与实验值的600±60 cm^（-1）吻合良好.另外计算中发现CH3Se在0.025 e V、3.661 e V和7.322 e V处存在1^2A＇→1^2A″、1^2A＇→2^2A＇（1^2A1）和1^2A＇→1^2A″三处比较强烈的激发光谱.

英文摘要：

Electronic states of the CH3 Se have been studied using the complete active space self-consistent field（ CASSCF） and multiconfiguration second-order perturbation theory（ CASPT2） methods in conjunction with ANO-RCC（ TZP） basis set. To investigate the Jahn-Teller effect on the CH3 Se radical,Cssymmetry was used for CH3 Se in calculations. The results showed that the Jahn-Teller effect is very small（ 69 cm^（-1）） and the 1^2A＇state is slightly more stable than 1^2A″（ 8 cm^（-1））. The computed C—Se stretching ν6（ a＇） frequency is 554. 1cm^（-1）which is in good agreement with the experimental values of 600 ± 60 cm^（-1）. The calculations of CH3 Se at3. 621 and 5. 307 e V are attribute to the 1^2A＇ → 2^2A＇（ 1^2A1） and 1^2A＇→ 2^2A″,respectively.