Single-Molecule Dissociation by Tunneling Electrons

The tunneling current from a scanning tunneling microscope was used to image and dissociate single ${\mathrm{O}}_2$ molecules on the Pt(111) surface in the temperature range of 40 to 150 K. After dissociation, the two oxygen atoms are found one to three lattice constants apart. The dissociation rate as a function of current was found to vary as $I^{0.8\pm 0.2}$, $I^{1.8\pm 0.2}$, and $I^{2.9\pm 0.3}$ for sample biases of 0.4, 0.3, and 0.2 V, respectively. These rates are explained using a general model for dissociation induced by intramolecular vibrational excitations via resonant inelastic electron tunneling.