A scanning tunneling microscope (STM) was used to control the pathway of the dissociation of single O2 molecules chemisorbed on Ag(110) at 13K. Tunneling of electrons from the STM tip into the O2 caused dissociation of the molecule, giving rise to two adsorbed O atoms separated along the [11¯0] direction. In contrast, the ejection of electrons from the O2 molecule produced adsorbed O atoms separated along the [001] direction. These results illustrate that control of the dissociation pathway and product formation are associated with a specific molecular orbital located at the Fermi level.

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The image of the O2(11¯0) molecule obtained using a bare tip exhibits a deeper oval-shaped depression than is observed in the image of the O2(001) molecule in Fig. 1(a). The two protrusions observed in the image of O2(001) in Fig. 1(b) (taken using a CO-terminated tip) are not observed in the image of O2(11¯0).

19.

Under the negative voltage pulse, 15% of the 138 O2(001) molecules examined showed a dissociation pathway the same as that found under a positive voltage pulse and 85% showed a different dissociation pathway.

20.

In the dissociation, 12% of the Osb atoms were found along the O–O bond direction of the parent O2(001). In contrast, Osb can be shifted along the [11¯0] direction, e.g., up by one lattice site as shown in Figs. 1(g)–1(i).

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