In paramagnetic compounds, the hyperfine interactions between the 2H nuclei and electron spins in paramagnetic ions should be incorporated to the Hamiltonian of Eq. (1). Neglecting the isotropic component from the Fermi- and pseudo-contact interactions, the hyperfine interaction can be given by the dipole coupling of nuclear–electron spins as
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where CQ = e2Qq=h is a parameter called a quadrupole coupling constant