For heteronuclear diatomic molecules, molecules composed from two different atomic nuclei, the internal partition function simply receives a factor of \(\xi\ns_{elec}\cdot\xi^{(1)}_{nuc}\cdot\xi^{(2)}...For heteronuclear diatomic molecules, molecules composed from two different atomic nuclei, the internal partition function simply receives a factor of ξ\nselec⋅ξ(1)nuc⋅ξ(2)nuc, where the first term is a sum over molecular electronic states, and the second two terms arise from the spin degeneracies of the two nuclei.
