  Vibronic spectra of molecules are typically described within the
Franck-Condon model. Here, we show that highly resolved vibronic spectra of
large organic molecules on a single layer of MoS$_{2}$ on Au(111) show spatial
variations in their intensities, which cannot be captured within this picture.
We explain that vibrationally mediated perturbations of the molecular wave
functions need to be included into the Franck-Condon model. Our simple model
calculations reproduce the experimental spectra at arbitrary position of the
STM tip over the molecule in great detail.
