A New Mechanism of Atomic Manipulation: Bond-Selective Molecular Dissociation via Thermally Activated Electron Attachment

We report a new mechanism of (bond-selective) atomic manipulation in the scanning tunneling microscope (STM). We demonstrate a channel for one-electron-induced C-Cl bond dissociation in chlorobenzene molecules chemisorbed on the Si(111)-7 x 7 surface, at room temperature and above, which Is thermally activated. We find an Arrhenius thermal energy barrier to one-electron dissociation of 0.8 +/- 0.2 eV, which we correlate explicitly with the barrier between chemisorbed and physisorbed precursor states of the molecule. Thermal excitation promotes the target molecule from a state where one-electron dissociation Is suppressed to a transient state where efficient one-electron dissociation, analogous to the gas-phase negative-ion resonance process, occurs. We expect the mechanism will be obtained in many surface systems, and not just in STM manipulation, but In photon and electron beam stimulated (selective) chemistry.