Scanning Tunnelling Microscopy (STM) is opening up a new field of reaction dynamics, followed one-molecule-at-a-time, only recently applied to reaction at a metal surface. Here we combine experiment with theory in studying the motions involved in the successive breaking by electron-induced reaction of the two carbon-halogen bonds, C-Cl or C-I, in physisorbed p-dihalobenzene, to form chemisorbed halogen-atoms and organic residue on Cu(110) at 4.6 K. We characterize the geometry of the physisorbed initial state, p-dichlorobenzene (pDCB) and p-diiodobenzene (pDIB), at the copper surface, as well as the successive final states of both chemisorbed reaction products: electron #1 giving rise to the first halogen-atom and a chemisorbed halophenyl and electron #2 giving a second halogen-atom and a chemisorbed phenylene. The major findings reported are (a) the distance and angular distributions of the chemisorbed reaction products relative to the physisorbed reagent molecule, (b) an approximate ab initio calculation, coupled with classical molecular dynamics (MD), of the repulsion between the products on the excited potential-energy surfaces, pes*, following excitation by electrons #1 or #2, and subsequently MD on the ground-state pes with inclusion of inelastic surface-interaction as a means to understanding the above, (c) observation of the changing dynamics with the chemistry of the halogen-atom, and (d) characterization of the effects of secondary encounters among the reaction products in the constrained space of the more highly localized reaction of pDIB. Item (d) shows clear evidence of high reactivity in surface-aligned collisions with restricted impact parameter, termed Surface Aligned Reaction, SAR, characterized by STM.

Energy‐deformation characteristics for the primary T, S, and U conformational units of tie molecules were obtained from the analysis of data generated from a constrained minimization algorithm. Energy‐deformation profiles (covering the range from compact equilibrium defect structures to the fully extended chain) are reported for the S0 and S1 members of the Sλ family and for the U00 member of the Umn family. Estimates of the energy content V0 and the elastic modulus E were obtained from the computed energy‐deformation data in the vicinity of the equilibrium Structure—S0 → {60°, 180°, −60°}, V 0italicS 0 = 1.7 kcal/mole, E italicS 0 = 60 kcal/cm3 [250 × 1010 dyn/cm2];S1 → {60°, 180°, 180°, 180°, −60°}: V 0italicS 0 = 1.7 kcal/mole, E italicS 1 = 25 kcal/cm3 [100 × 1010 dyn/cm2]; and U00 → {60°, 180°, 60°, 180°, 60°}: V 0italicU 00 = 2.7 kcal/mole, E italicU 00 = 80 kcal/cm3 [340 × 1010 dyn/cm2]. Although the elastic modulus of the U00 unit is comparable to the elastic modulus of the fully extended chain, the highenergy content of this unit (V0 = 2.7 Kcal/mole) prohibits a significant population and thereby mitigates an appreciable reinforcing effect from this rigid unit. A model for a surrogate force constant is introduced to generalize the results from this study to any member of the Sλ or Umn family as well as any combination of Sλ and Umn units. This generalization provides a basis for estimating the deformation characteristics of tie molecules comprised of various populations of these primary conformational building blocks.

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A novel sample holder that enables atomic force microscopy (AFM) tips to be mounted inside a scanning electron microscopy (SEM) for the purpose of characterizing the AFM tips is described. The holder provides quick and easy handling of tips by using a spring clip to hold them in place. The holder can accommodate two tips simultaneously in two perpendicular orientations, allowing both top and side view imaging of the tips by the SEM.