多组态二级微扰理论计算CH3O2激发光谱以及CH3O2→CH3＋O2解离反应

在C_s对称性和aug-cc-pVTZ基组水平下, 采用全活化空间自洽场方法(CASSCF)研究了CH₃O₂自由基基态及其阴阳离子的12个低激发态. 为了进一步考虑动态电子相关效应, 采用二级多组态微扰理论(CASPT2)获得更加精确的能量值. 所有计算得到的电子态都是价电子态, 而且所得绝热激发能和电子亲和势与实验值非常接近.在CASPT2//CASSCF理论水平下计算了CH₃O₂从²A"和²A'电子态的CH₃O₂→CH₃＋O₂的解离反应的势能曲线(PECs). 优化得到的裂解产物的几何结构和能量与分别优化CH₃和O₂得到的结果进行比较, 从而确定裂解产物的电子态. 结果表明, 从²A"和²A'电子态的解离反应分别对应产物CH₃(²A")＋O₂(³A")和CH₃(²A")＋O₂(¹A").

Excited Spectroscopy and O2-loss Dissociations in Low-lying Electronic States of CH3O2 Studied Using Multiconfiguration Second-Order Perturbation Theory

Complete active space self-consistent field (CASSCF) calculations with aug-cc-pVTZ basis sets were performed for twelve low-lying electronic states of the methyl peroxy radical CH_3O_2 and its positive and negative ions in Cs symmetry. The accuracy of the energies were improved by including dynamic elec- tron correlation by the multiconfiguration second-order perturbation theory (CASPT2) method. All calcu- lated states are valence states. The calculated adiabatic excitation and affinity energies are in reasonable agreement with the experimental data. Potential energy curves (PECs) for O_2-loss dissociation from the 2A" and 2A' states were calculated at the CASPT2//CASSCF level and the electronic states of the O_2 and CH3 as the dissociation products were carefully determined by checking the relative energies and geometries of the asymptote products along the PECs. The O_2-loss PEC calculations for CH_3O_2 indicate that O_2-loss dissocia- tion occurs from the 2A" and 2A' states leading to CH3(2A") O_2(3A") and CH3(2A") O_2(1A"), respectively.