Broadband Tunable Electron Paramagnetic Resonance Spectroscopy of Dilute Metal Complexes

Analysis of the electron paramagnetic resonance (EPR) of transition ion complexes requires data taken at different microwave frequencies because the spin Hamiltonian contains operators linear in the frequency as well as operators independent of the frequency. In practice, data collection is hampered by the fact that conventional EPR spectrometers have always been designed to operate at a single frequency. Here, a broadband instrument is described and tested that operates from 0.5 to 12 GHz and whose sensitivity approaches that of single-frequency spectrometers. Multifrequency EPR from triclinic substitutional (0.5%) Cu(II) in ZnSO₄ is globally analyzed to illustrate a novel approach to reliable determination of the molecular electronic structure of transition ion complexes from field-frequency 2D data sets.