Hyperfine Splitting of the Interaction Energy in H + D and in D + D

The hyperfine interaction of a ground‐state D atom with either a ground‐state H or a ground‐state D atom is treated. For H + D there are 24 hyperfine states with 12 potential‐energy curves, and for D + D there are 36 hyperfine states with 22 potential‐energy curves. At separations greater than ${\text{9a}}_0$ to ${\text{10a}}_0$ , the electronic spins (for most of these hyperfine states) become partially decoupled and one can no longer refer to the molecule as being an electronic singlet or an electronic triplet.