甲氧基取代的半醌自由基和质子超精细耦合常数的非限制Hartree-Fock计算

Unrestricted Hartree-Fock Calculations of Methoxyl Substituted Semiquinone Radicals and the Proton Hyperfine Coupling Constants

利用从头算非限制Hartree-Fock方法,分别计算了甲氧基取代的对一半醌和对一氢化半醌系列的不同组份的自旋密度,用经验的McConnell关系估算了电子自旋共振(ESR)实验测定的质子各向同性超精细分裂。结果表明,理论计算符合较好,经验的加和性规则不灵。为了解释醌环上两个相邻甲氧基取代基的ESR的异常测定值,必须考察溶剂效应。利用投影算符技巧讨论了有关解释得自非自旋本征态的非限制Hartree-Fock波函数的自旋密度的基本问题。得到的各体系的UHF波函数几乎全为纯的双重态。

Spin densities are calculated for various members of the family of methoxyl-substituted p-se mi and p-hydrosemiquinones using the ab initio unrestricted Hartree-Fock method, respectively. The empirical McConnell relation has been applied to estimate from certain results of proton iso-tropic hyperfine splittings measured in electron spin resonance (ESR) experiments. It is shown that the principle of correlative additivity, which in general accurately describes the changes in the hyperfine coupling constants is violeted. The breakdown of this concept, however, is not observed when the theoretically calculated spin densities are used. Therefore, solvent effects need to be consi. dered. Furthermore, the general opinion of the interpretation of spin-densities obtained from an unrestricted Hartree-Fock wave function which is not an eigenstate of spin is discussed using a projection operator technique. From the results it is obvious that the UHF wave function obtained for all systems nearly corresponds to the pure doublet spin state.