Field dependence of R in the absence (a) and in the presence of axial ZFS (D=0.1 cm−1) for a proton along the z axis (b) or in the x,y plane (c), and in the presence of ZFS with maximal rhombicity (E/D=1/3, D=0.1 cm−1) for a proton along the z axis (d) or in the x,y plane (e) (S=3/2, τ=1 ns).