Single-molecule surface reaction by tunneling electrons

Scanning tunneling microscope images of isolated molecules of trans-2-butene (C4H8) and 1,3-butadiene (C4H6) adsorbed on the Pd(1 1 0) surface are presented at 4.7 K. The former appears as a dumbbell-shaped protrusion perpendicular to the Pd row, while the latter appears as an elliptical protrusion parallel to the Pd row. By dosing tunneling electrons, the trans-2-butene molecule is transformed into a 1,3-butadiene molecule via dehydrogenation reaction. The threshold voltage (∼365 mV) is so small that the electronic excitation to the C–H antibonding state cannot be attributed to the mechanism. Instead, we consider that the multiple excitation of C–H stretching mode by inelastically tunneled electron is responsible for the dehydrogenation.