Electric Field Gradient and Magnetic Spin-Spin Interactions in Isotopes of the Hydrogen Molecule

Field gradients have been calculated at 12 values of the internuclear distance from 34-, 66-, and 87-term molecular wave functions expanded in prolate-spheroidal coordinates and r₁₂. Convergence of the gradients as the basis enlarges is indicated and the dissociation energy of H₂ is in agreement with experiment. Using vibrationally averaged gradients, experimental values for the quadrupole-interaction constant, and estimating the error in the field gradients arising from truncation of the basis, the electric quadrupole moment of the deuteron is found to be 0.2875±{}0.002×{}10^-26 cm², which is 2% larger than the most recent values. This disagreement as well as that among earlier authors is explained. First-order perturbation-theoretic results for the magnetic spin-spin interaction constant for H₂(J=1), HD(J=1), D₂(J=1), and D₂(J=2) are in agreement with experiment and, except for H₂, well inside experimental error.