A scanning tunneling microscope was used to perform inelastic electron tunneling spectroscopy on single Cu(II) etioporphyrin-I molecules. The resulting vibrational spectra showed an increase in ac tunneling conductance at 359 mV. This change was attributed to the vibrational excitation of the methene bridge C–H stretch mode. Vibrational microscopy was used to image the spatial distribution of the inelastic tunneling channels involved in this excitation.

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