  Geometric symmetries cause orbital degeneracies in a molecule's spectrum. In
a single-molecule junction, these degeneracies are lifted by various
symmetry-breaking effects. We study quantum transport through such
nanostructures with an almost degenerate spectrum. We show that the master
equation for the reduced density matrix must be derived within the
singular-coupling limit as opposed to the conventional weak-coupling limit.
This results in signatures of the density matrix's off-diagonal elements in the
transport characteristics.
