HYPERFINE LINE SHIFT IN THE EPR-SPECTRA OF RANDOMLY ORIENTED CU(II) CONTAINING SYSTEMS WITH AXIAL SYMMETRY

We revisit the problem of unequal spacing of the hyperfine lines in th e g parallel to region of the experimental EPR spectra of some type 2 Cu(II) complexes displaying axial symmetry. This shift, already reprod uced by our computer simulation model, cannot be justified fully in th e framework of second-order perturbation theory. On this ground, we ha ve performed an analysis, based on a computer simulation approach, of all the possible causes that can give rise to a shift of the hyperfine lines. The results show that in randomly oriented samples the overall high field lineshift is due to a superposition of Gaussian-like hyper fine lines and the background arising from the presence of different o rientations of the paramagnetic ions with respect to the magnetic fiel d. In addition, the effect induced on the EPR spectra by a superpositi on of adjacent hyperfine lines is discussed in connection with the dis tortion of the g parallel to pattern registered in the EPR spectra of some type 1 Cu(II) complexes. As a final remark, our analysis shows th at a computer simulation approach is required to extract reliable valu es for the spin Hamiltonian parameters from the experimental EPR spect ra of randomly oriented paramagnetic samples.