G-FACTOR OF CU2+ WITH (2)A(1G) GROUND-STATE

In this paper the perturbation expressions of the g(z) and g(x) factor s of the 3d(9) ions with (2)A(1g) ground state in a tetragonal crystal field are obtained by a molecular orbital approach. Using these formu lae the g(z) and g(x) factors of the NH4X:Cu2+ (X=Cl, Br, I) crystals are calculated. The results show that the contribution of the spin-orb it coupling from ligands is small for the Cu2+-Cl- cluster but signifi cant for the Cu2+-I- cluster. The theoretical difficulties of pure cry stal-field model in these compounds, namely the sign of the Delta g(z) (=g(z)-g(s)) in NH4I:Cu2+ being opposite to the experimental, and the order of the g(z) (zeta(d)) (NH4Cl:Cu2+ > NH4Br:Cu2+ > NH4I:Cu2+) bei ng opposite to the measured one (NH4Cl:Cu2+ < NH4Br:Cu2+ < NH4I:Cu2+), hence removed.