Tunneling mode selectivity

Fehrensen B, Luckhaus D and Quack M 1999 Mode selective stereomutation tunnelling in hydrogen peroxide isotopomers Chem. Phys. Lett. 300 312-20... 

B. Fehrensen, D. Luckhaus, M. Quack, M. Willeke, and T. R. Rizzo, Ab initio calculations of mode selective tunneling dynamics in 12CH3OH and 13CH3OH. J. Chem. Phys. 119,5534 5544... 

C. Manca, C. Tanner, S. Coussan, A. Bach and S. Leutwyler, H atom transfer along an ammonia chain Tunneling and mode selectivity in 7-hydroxyquinoline-(NH3)3, J. Chem. Phys., 121 (2004) 2578-2590. 

Keywords Vibrational spectroscopy scanning tunneling microscopy and spectroscopy conductance inelastic conductance single-molecule chemistry controlled manipulation mode-selective reactivity. 

Figure Bl.4.9. Top rotation-tunnelling hyperfine structure in one of the flipping inodes of (020)3 near 3 THz. The small splittings seen in the Q-branch transitions are induced by the bound-free hydrogen atom tiiimelling by the water monomers. Bottom the low-frequency torsional mode structure of the water duner spectrum, includmg a detailed comparison of theoretical calculations of the dynamics with those observed experimentally [ ]. The symbols next to the arrows depict the parallel (A k= 0) versus perpendicular (A = 1) nature of the selection rules in the pseudorotation manifold.

The high sensitivity of tunneling spectroscopy and absence of strong selection rules allows infrared and Raman active modes to be observed for a monolayer or less of adsorbed molecules on metal supported alumina. Because tunneling spectroscopy includes problems with the top metal electrode, cryogenic temperatures and low intensity of some vibrations, model catalysts of evaporated metals have been studied with CO and acetylene as the reactive small molecules. Reactions of these molecules on rhodium and palladium have been studied and illustrate the potential of tunneling spectroscopy for modeling reactions on catalyst surfaces,... 

Inelastic tunnelling electrons can also be used to selectively induce either the translation over a metallic surface or desorption from the metallic surface of individual molecules, as has been shown for NH3 on Cu(lOO) surfaces (Pascual et al, 2003). Activation of either the stretching vibration of ammonia ( 408 meV) leading to lateral translation on the surface, or the inversion of its pyramidal structure (umbrella mode s(NH3) 139 meV) leading to desorption, can be achieved by adjusting 7t and Vt. 

The most common STM mode of operation is the constant current mode, where the bias voltage ( tens of millivolts to several volts) is held constant while the feedback circuit connected to the z piezo electrode moves the tip up and down to maintain a fixed pre-selected tunneling current (distance). At each point along each scan line in the x, y raster pattern, the current is measured and compared to the operator-chosen set-point current (typically tens of... 

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