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Existing theories of the relative dipole moments in singlet and triplet states have been re-examined, and calculations are presented for NH, CH2 and a fictitious molecule with nuclear charges 1.1 and 0.9 au. The usual assumption that electrons are farther apart in the triplet is found to be questionable. Changes in inner molecular orbitals are also more important than was believed previously.

It is shown that for H+2 and its isotopes, the electronic Schrodinger equation involving the electron rest mass me can be related in a simple way to that involving the electron reduced mass μe = me(ma + mb)/(me + ma + mb) by a straight-forward scaling of all distances in the first of these equations by μe/me. A numerical comparison of the two approaches is made at the adiabatic level of approximation for HD+, and it is seen that any differences would have only a negligible effect on the calculated vibration-rotation spectrum.