Spatial imaging of individual vibronic states in the interior of single molecules

Abstract

Selective excitations of specific vibronic modes in position space are realized in single naphthalocyanine molecules adsorbed on an ultrathin alumina film by a scanning tunneling microscope at low temperature. Distinct spatial distributions are imaged for the different vibronic modes, which are in accordance with spectra recorded over different points of the molecule and its orbital structure. These distinct vibronic images, together with the differential conductance images and calculated molecular orbitals, lead to vibrational excitations that are associated with the doubly degenerate lowest unoccupied molecular orbitals (LUMO)--LUMO-α and LUMO-β. These results reveal the presence of different molecular conformations on the surface and the nature of the electron-vibrational coupling.