Vibrational Excitation Induces Double Reaction

Abstract

Electron-induced reaction at metal surfaces is currently the subject of extensive study. Here, we broaden the range of experimentation to a comparison of vibrational excitation with electronic excitation, for reaction of the same molecule at the same clean metal surface. In a previous study of electron-induced reaction by scanning tunneling microscopy (STM), we examined the dynamics of the concurrent breaking of the two C-I bonds of ortho-diiodobenzene physisorbed on Cu(110). The energy of the incident electron was near the electronic excitation threshold of E0=1.0 eV required to induce this single-electron process. STM has been employed in the present work to study the reaction dynamics at the substantially lower incident electron energies of 0.3 eV, well below the electronic excitation threshold. The observed increase in reaction rate with current was found to be fourth-order, indicative of multistep reagent vibrational excitation, in contrast to the first-order rate dependence found earlier for electronic excitation. The change in mode of excitation was accompanied by altered reaction dynamics, evidenced by a different pattern of binding of the chemisorbed products to the copper surface. We have modeled these altered reaction dynamics by exciting normal modes of vibration that distort the C-I bonds of the physisorbed reagent. Using the same ab initio ground potential-energy surface as in the prior work on electronic excitation, but with only vibrational excitation of the physisorbed reagent in the asymmetric stretch mode of C-I bonds, we obtained the observed alteration in reaction dynamics.

On-surface generation and imaging of arynes by atomic force microscopy

“…However, adjusted constant-height AFM images 40 , presented in Fig. 5f, reveal that the outermost ring is, indeed, present, but bent towards the surface, that is, the aryne immediately forms strong covalent bonds to the Cu surface, in agreement with previous studies on dehydrogenated phthalocyanine molecules 23 and benzyne adsorbed on other metal surfaces 32,46 .…”

Desorption induced by low energy charge carriers on Si(111)‐7 × 7: First principles molecular dynamics for benzene derivates

“…Scanning tunneling microscopes (STM) made the manipulation of singe atoms and molecules on surfaces possible . Apart from mechanical interactions and purely field induced processes, such manipulations usually proceed via inelastic electron tunneling (IET) .…”

“…Scanning tunneling microscopes (STM) made the manipulation of singe atoms and molecules on surfaces possible. [1][2][3][4] Apart from mechanical interactions and purely field induced processes, such manipulations usually proceed via inelastic electron tunneling (IET). [5] Here, electrons or holes often transiently occupy short lived donor or acceptor states at the adsorption site, so called ion resonances.…”

High-Voltage-Assisted Mechanical Stabilization of Single-Molecule Junctions

“…This mechanical instability often limits experiments on single molecule junctions to the off-resonant tunneling regime. In order to combine the desired features of efficient resonant transport at high voltage operation with mechanically stable molecules, one needs to determine which experimentally controlled parameters contribute to the mechanical stability of molecules under non-equilibrium transport conditions.Charge transport induced bond rupture was observed for physisorbed molecules in scanning tunneling microscope experiments [9][10][11] as well as in atomic chains [12] and single molecule junctions [3,4,13], where the molecules are chemically bonded to the leads. In particular, the occurrence of bond rupture increased with increasing bias voltage, which points to the increased transport induced charging of the molecule.…”