On the operator equivalents and the crystal-field and spin Hamiltonian parameters

Operator equivalents used in magnetic resonance (electron paramagnetic resonance EPR], electron-nuclear double resonance, nuclear magnetic resonance, etc.) are considered. The known non-Hermitian tensor operators O _±q ^(k) (0 ≤ q ≤ k) defined by D. Smith and J. H. M. Thornley (Proc. Phys. Soc. 89, 779–781, 1966) after H. A. Buckmaster (Can. J. Phys. 40, 1670–1677, 1962) are expressed in terms of Hermitian cosine and sine operators O _kq ^c and O _kq ^s. These new normalized operators are related to the nonnormalized extended Stevens operators O _k ^q and O _k ^−q ≡ Ω _k ^q defined by C. Rudowicz (J. Phys. C.: Solid State Phys. 18, 1415–1430, 1985), which are commonly used in EPR of transition ions. The relations between O _kq ^c,s and some other normalized operators occurring in the literature are also given. New crystal-field or spin Hamiltonian parameters B _kq ^c and B _kq ^s associated with the corresponding operators O _kq ^c and O _kq ^s are discussed.