Single-Electron Induces Double-Reaction by Charge
Delocalization
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Abstract
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)