The perusing excavating microscope enables atomic scale measurements of electron transference over individual molecules. Copper phthalocyanine and magnesium porphine molecules adsorbed on a thin oxide film grown on the NiAl(110) surface were probed. The single-molecule intersections contained two excavating barricades, vacuum gap, and oxide film. Differential conductance spectroscopy shows that electron transference occurs via vibronic states of the molecules. The intensity of spectral peaks corresponding to the individual vibronic states depends on the relative electron excavating tariffs over the two barricades of the junction, as found by varying the vacuum gap excavating rate by changing the height of the perusing excavating microscope tip above the molecule. A simple, progressive excavating prototypical explains the observed trends.