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(110) 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 I'd row. By dosing tunneling electrons, the trans-2-butene molecule is transformed into a 1,3-butadiene molecule via dehydrogenation reaction. The threshold voltage (similar to365 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. (C) 2002 Elsevier Science B.V. All rights reserved.