Line-Shape Analysis in EPR Spectra of Nb(IV) Complexes in Solutions and Glasses

Abstract

The EPR spectra of a Nb (IV) complex in alcoholic liquid and solid solution are investigated between 293° and 77°K. The spectra exhibit hyperfine structure originating from interaction of one single 4d electron with the central Nb( $\mathrm{I=}\frac{9}{2}$ ) nucleus. At 77°K the spectra show a complicated appearance. In order to analyze the observed spectra a formula for the line shape is derived by assuming a Lorentzian shape function, axial symmetry of both the g and a tensor, and completely randomized orientation of the complexes. With the correct transition probabilities and a certain approximation for the resonance field a closed expression for the line shape of a single hyperfine structure line is given, which readily lends itself to numerical calculation. By use of a computer program the components of the g and a tensor are determined for three different alcohols, methanol, ethanol, and isopropanol, as solvents (see Table IV). It is shown that satisfactory agreement between observed and calculated spectra can only be obtained if anisotropy of the Lorentzian line‐shape parameter is assumed besides the well‐known dependence of this parameter on the magnetic quantum number m.