The zero-field EPR spectrum of a copper dimer

The zero-field epr spectrum of [Cu(C6H5CO2)2(C6H5CO2H)]2 at 95 K is reported. Analysis of the spectrum in terms of a spin Hamiltonian which includes zero-field splitting and average hyperfine constants for the isotopes 63Cu and 65Cu accounts well for the spectrum and gives llip;D… = 9.979 GHz, …E… = 0.195 GHz, …A…… = 222 MHz, …A⊥… = 39 MHz and a line width of 27 MHz. A qualitative interpretation is given in terms of an idealized Hamiltonian in which A⊥=0.0. This model shows that the nuclear quadrupole term has no effect on the spectrum. The model is also used to develop some simple rules for estimating spin Hamiltonian parameters directly from such spectra.