Lash Miller Chemical Laboratories, Department of Chemistry and Institute of Optical Sciences, University of Toronto, 80 St. George Street, Toronto, Ontario, M5S 3H6 Canada.
J Am Chem Soc. 2013 Apr 24;135(16):6220-5. doi: 10.1021/ja400612c. Epub 2013 Apr 12.
Injecting an electron by scanning tunneling microscope into a molecule physisorbed at a surface can induce dissociative reaction of one adsorbate bond. Here we show experimentally that a single low-energy electron incident on ortho-diiodobenzene physisorbed on Cu(110) preferentially induces reaction of both of the C-I bonds in the adsorbate, with an order-of-magnitude greater efficiency than for comparable cases of single bond breaking. A two-electronic-state model was used to follow the dynamics, first on an anionic potential-energy surface (pes*) and subsequently on the ground state pes. The model led to the conclusion that the two-bond reaction was due to the delocalization of added charge between adjacent halogen-atoms of ortho-diiodobenzene through overlapping antibonding orbitals, in contrast to the cases of para-dihalobenzenes, studied earlier, for which electron-induced reaction severed exclusively a single carbon-halogen bond. The finding that charge delocalization within a single molecule can readily cause concerted two-bond breaking suggests the more general possibility of intra- and also intermolecular charge delocalization resulting in multisite reaction. Intermolecular charge delocalization has recently been proposed by this laboratory to account for reaction in physisorbed molecular chains (Ning, Z.; Polanyi, J. C. Angew. Chem., Int. Ed. 2013, 52, 320-324).
通过扫描隧道显微镜将电子注入物理吸附在表面的分子中，可以诱导吸附键的离解反应。在这里，我们通过实验表明，单个低能电子入射到物理吸附在 Cu(110)上的邻二碘苯上，优先诱导吸附物中两个 C-I 键的反应，其效率比可比的单键断裂情况高出一个数量级。我们使用了一个双电子态模型来跟踪动力学，首先在阴离子势能面（pes*）上，随后在基态 pes 上。该模型得出的结论是，双键反应是由于邻二碘苯中相邻卤素原子之间的附加电荷通过重叠的反键轨道而离域，这与之前研究过的对二卤代苯不同，后者的电子诱导反应仅切断单个碳-卤键。发现单个分子内的电荷离域可以轻易地导致协同的双键断裂，这表明更普遍的可能性是分子内和分子间的电荷离域导致多部位反应。本实验室最近提出，分子间电荷离域可以解释物理吸附分子链中的反应（Ning, Z.; Polanyi, J. C. Angew. Chem., Int. Ed. 2013, 52, 320-324）。
