“…The hyperfine interaction between the electron and nuclear spin is represented by the second term of eq 1. The second rank tensor T that describes this interaction can be resolved into isotropic and anisotropic components. The effective Hamiltonian for the hyperfine interaction is then given by 3Chfs = AS-I + S-B-I (2) and the isotropic and anisotropic components of T correlate with the first and second terms, respectively, of eq 2. In eq 2 the first term is the Fermi or contact interaction and arises from the overlap of the nuclear and unpaired electron wave functions. This term was introduced by Fermi in the treatment of atomic hyperfine interaction, and he showed that the constant A is related to the value of the normalized wave function of the unpaired electron at the nucleus…”