Investigations in Many-Body Perturbation Theory of Hyperfine Structure in Diatomic Molecules

The linked-cluster many-body perturbation theory has been applied to small heteronuclear diatomic molecules using a variational Hartree—Fock molecular-orbital basis set. This procedure has been applied to study the isotropic hyperfine interaction in the ${}_{}{}^2{}_{}{}^{}\Pi$ ground state of the free radical ${\mathrm{O}}^{17}$H and to the magnetic shielding of ${\mathrm{H}}^1$ and ${\mathrm{F}}^{19}$ in the HF molecule. These investigations have led to a number of physical conclusions about the influence of correlation and exchange polarization effects on the isotropic hyperfine interactions in OH. The calculated shielding parameters and hyperfine constants were found to be in better than 15% agreement with experimental data wherever available.