Spin-Hamiltonian input parameters in the ESR analysis of liquid phase copper complexes

Electron paramagnetic resonance (EPR) spectra of the copper complex of bis(dimethyldithiocarbamato) copper (II) [65Cu(dtc)2] in the liquid phase (o-toluidine at 20 °C, η≃4.39 cP) have been obtained at five widely varying microwave frequencies: 1.19, 2.51, 3.44, 9.12, and 34.78 GHz. A two-stage procedure has been developed for analysis of these spectra under assumptions of coincident axial magnetic tensors and isotropic rotational diffusion. In the first stage, linewidths, and dynamic second-order frequency shifts are extracted from the spectra. Algebraic manipulation of motional narrowing linewidth and shift equations yields preliminary values for the magnetic parameters and the rotational correlation time together with error estimates. In the second stage, full spectral simulations are made in which goodness-of-fit is optimized over the multidimensional space that is determined by these preliminary values and errors. The first stage is only possible by inclusion of dynamic second-order shifts; a unique solution cannot be obtained from linewidth data alone. Using this procedure, effective rigid-limit parameters have been obtained from liquid-phase data alone. The assumption that these parameters are the same in frozen solution and in the liquid phase is avoided. The high quality of the simulations over a wide range of microwave frequencies gives confidence in the theoretical formulation. © 1984 American Institute of Physics