Examination of the various crystal field theories of d<SUP>3</SUP> ions in trigonal fields

Zero-field splitting and g-anisotropy of the ground multiplet of HfS<SUB>2</SUB>(V<SUP>2+</SUP>) have been measured by electron paramagnetic resonance. The unusually large g-anisotropy and its relationship to the zero-field splitting alow a comparison between various crystal field theories. We find that the experimental results are in disagreement with the simple crystal field theory of Van Vleck for the ground multiplet of d<SUP>3</SUP> ions in trigonally distroted octahedral environments, but in reasonable agreement with the more elaborate but straightforward crystal field theory of Macfarlane. We thus conclude that it is unnecessary to resort to an anisotropic spin-orbit coupling as suggested by Sugano and Tanabe or to odd-parity crystal field terms as suggested by Artman and Murphy