  Negative differential conductance (NDC) is a non-linear transport phenomenon
ubiquitous in molecular nanojunctions. Its physical origin can be the most
diverse. In rotationally symmetric molecules with orbitally degenerate
many-body states, it can be ascribed to interference effects. We establish in
this paper a criterion to identify the interference blocking scenario by
correlating the spectral and the topographical information achievable in an STM
single molecule measurement. Simulations of current voltage characteristics and
current maps for a Cu-Phthalocyanine (CuPc) on a thin insulating film are
presented as experimentally relevant examples.
