Molecular rotation induced by inelastic electron tunneling

Electron tunneling from a scanning tunneling microscope tip has recently be en shown to induce reversible rotation of O-2 molecules chemisorbed on Pt(1 11) [B. C. Stipe ct al., Science 279, 1907 (1998)]. This process is interpr eted as proceeding via the transient capture of the tunneling electron by t he adsorbate. A finite angular momentum can be transferred in a resonant el ectron-molecule scattering, leading to an efficient rotational excitation. This process is a direct consequence of the electronic structure of the res onance and of angular momentum conservation; it does not require a long res onance lifetime to be efficient.