Molecular Dynamics of the Electron-Induced Reaction of Diiodomethane on Cu(110)

Diiodomethane is used to generate C1 fragments at surfaces, en route to higher hydrocarbons. Here scanning tunneling microscopy was employed to examine the interaction of diiodomethane, CH2I2, with a Cu(110) surface, from 4.6 to 8.8 K. In this temperature range unexpectedly rapid thermal reaction resulted in the rupture of two C–I bonds, yielding pairs of I atoms recoiling in opposite directions. Approximately 65% of the carbene, CH2, product from this highly exothermic (4.1 eV) thermal reaction remained chemisorbed. Two stable physisorbed configurations of diiodomethane were found, “vertical” (75%) and “horizontal” (25%). Electron-induced reaction of these intact adsorbates led to single-electron dissociation of both the C–I bonds, with a minor path leading to single bond breaking to form CH2I. Directed recoil of chemisorbed carbene was observed in approximately half the electron-induced reactive events. Simulation of the electron-induced reaction by the impulsive two-state (I2S) model consistently predi...