Investigation of Variations of Isotropic g- and A- Values with Orientation of Trapped O2−, N2− and Cl2− Radicals in KCl and NaCl Crystals

We have theoretically studied the electron paramagnetic resonance (EPR) properties of paramagnetic O2 − , N2 − and Cl2 − centers in the KCl and NaCl crystals. The calculations have been performed by the density functional theory (DFT) method with the B3LYP correlation functional at 6-31 G(d) level. The attention has been focused on the calculation of the variations of the EPR parameters such as the isotropic g- and A-values. These parameters were satisfactorily calculated for all three species with the orientation of the trapped radicals along all three axes of the crystals for the first time. Namely the molecular axis of the paramagnetic anions was oriented along the x, y and z directions of the crystallographic axes, which can experimentally never be done, and the variations of the EPR parameters were theoretically determined and analyzed as if the each of them is a tensor. And then their principal values and direction cosines were obtained. It was concluded that the anisotropy of the g- and A-values increases while the bond length of the molecular anion radical increases.