Stretched overlapping molecules

An interesting application of these principles is the prediction of CO dissociation routes on the closed-packed (111) surface of rhodium (see Fig. A.17). Two factors determine how the dissociation of a single CO molecule proceeds. First, the geometry of the final situation must be energetically more favorable than that of the initial one. This condition excludes final configurations with the C and the O atom on adjacent Rh atoms, because this would lead to serious repulsion between the C and O atoms. A favorable situation is the one sketched in Fig. A.17, where initially CO occupies a threefold hollow site, and after dissociation C and O are in opposite threefold sites. The second requirement for rupture of the CO molecule is that the C-0 bond is effectively weakened by the interaction with the metal. This is achieved when the C-O bond stretches across the central Rh atom. In this case there is optimum overlap between the d-electrons of Rh in orbitals, which extend vertically above the surface, and the empty antibonding orbitals of the CO molecule. Hence, the dissociation of CO requires a so-called catalytic ensemble of at least 5 Rh atoms [8,21,22]. 

The fundamental vibrations (8 stretching, 10 deformation and 3 torsional modes) of tri-fluoromethyl peroxynitrate (1) can be assigned from the FUR spectrum in the gas phase and FT-Raman spectrum of the liquid. The high-frequency stretching modes are characteristic and easily assigned, except for the Vs(CF3) and Vs(N02) fundamental modes, which overlap in the gas-phase IR spectrum. Near agreement is obtained between the experimental and the theoretically calculated vibrational spectra°°. Due to the Cj symmetry of the molecule, all the fundamental modes (7 stretching, 8 deformation and 3... 

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