General description of nuclear interaction terms in a spin Hamiltonian including a system of ligands

Abstract

Following a procedure described by R. Calvo ( J. Magn. Reson. 26 (1977)) to construct the ligand hyperfine terms contributing to the spin Hamiltonian of isolated paramagnetic centers, the second-rank terms in nuclear spin operators are derived with reference to a system of C 4 v symmetry. It is shown that these describe appropriately quadrupolar as well as coupling effects between different nuclei. The symmetry is automatically reflected in fixing the number of independent parameters demanded by the addition of such interactions, without new requirements from the group theory point of view. The matrices representing these effects in a six-atom cluster of C 4 v symmetry are explicitly given as an example.