EPR G TENSOR OF FREE RADICALS THEORY

自旋哈密顿参数的理论计算是非常重要的 不仅在确定结构方面有用，而且在 生物体系中自由基的识别。特别是，我们 最感兴趣的是预测g张量的值，因为 G-张量是从以下位置获得的主要信息 高频EPR。的详细信息。 具有G-张量结构的根，其结构可以是 阐明，不同的自由基可以区分，并具有溶剂性 效果已被测量。使用半经验MO方法(AM1和PM3)，我们可以 对超精细张量和g张量进行非常好的近似。这些 计算主要受基数设置的好坏的限制 确定自旋密度分布。在大多数情况下， 自旋密度的确定相当准确地由这样的半经验 方法，但也有许多例外，特别是西格玛 根和某些非平面圆周率根。更明确的结果 可以通过ab ini tio计算得到。因为大的 为扩展基集生成的C.I.状态的数量，我们是 目前仅限于小分子。利用摄动方法，我们 计划将我们的g张量计算扩展到大分子。这是 一个正在进行的项目。

Theoretical calculations of spin-Hamiltonian parameters are very useful not only in determination of structure but also in the identification of radicals in biological systems. In particular, we are most interested in predicting values of the g-tensor, since the g-tensor is the primary piece of information obtained from high-frequency EPR. With detailed information on variation of the g-tensor with structure of the radical, the structure can be elucidated, different radicals can be distinguished, and solvent effects gauged. With semi-empirical MO methods (AM1 and PM3), we can make very good approximations of the hyperfine and g-tensors. These calculations are primarily limited by how well the basis set determines the spin-density distribution. In most cases the spin-density is determined fairly accurately by such semi-empirical methods, but there are also many exceptions, particularly sigma radicals and certain non-planar pi radicals. More definitive results can be obtained from ab ini tio calculations. Because of the large number of C. I. states generated for extended basis sets, we are currently limited to small molecules. Using perturbation methods, we plan to extend our g-tensor calculations to large molecules. This is an ongoing project.