Action spectra associated with inelastic two-electron tunneling through a single molecule: Propene on Cu(211)

Inelastic electron tunneling through single molecules located in the tunnel junction between a surface and the tip of a scanning tunneling microscope may cause molecular surface dynamics. Vibrations excited by inelastically tunneling electrons may couple to other vibrational modes and finally induce processes like hopping or rotation. The reaction yield Y(V) as a function of a bias voltage V depict quasi an action spectrum of a certain dynamic event. Experimental results of action spectra are reproduced for rotation and hopping of a single propene molecule on a stepped Cu(211) surface. The good agreement between calculated and experimental Y(V) identify the respective vibrational modes excited by tunneling electrons. These induce then motions via intermode-coupling with the reaction coordinate modes. A general formula of a reaction rate R(V) in a two-electron process, exciting two different vibrational modes for enantiomer conversion of a single propene molecule is derived and the expected R(V) is calculated.