  We present a qualitative model for a fundamental process in molecular
electronics: the change in conductance upon bond breaking. In our model a
diatomic molecule is attached to spin-polarized contacts. Employing a Hubbard
Hamiltonian, electron interaction is neglected in the contacts and explicitly
considered in the molecule, enabling us to study the impact of electron
interaction on the molecular conductance. In the limit where the electron
repulsion is strong compared to the binding energy (as it becomes the case upon
dissociation) electron transmission in strongly suppressed compared to the
non-interacting case. However, the spin-polarized nature of the contacts
introduces a coupling between the molecular singlet and triplet states. This
coupling in turn yields additional resonances in the transmission probability
that significantly reduce the energetic separation appear between resonances.
The ramifications of our results on transport experiments performed on
nanowires with inclusions $H_2$ are discussed.
