Adsorbate geometries

Two other examples will sufhce. Methane physisorbs on NaCl(lOO) and an early study showed that the symmetrical, IR-inactive v mode could now be observed [97]. In more recent work, polarized FTIR rehection spectroscopy was used to determine that on being adsorbed, the three-fold degeneracies of the vs and v modes were partially removed [98]. This hnding allowed consideration of possible adsorbate-adsorbent geometries one was that of a tripod with three of the methane hydrogens on the surface. The systems were at between 4 and 40 K so that the equilibrium pressure was very low, about 10 atm. 

Wang J, Robinson IK, Ocko BM, Adzic RR. 2005. Adsorbate-geometry specific subsurface relaxation in the CO/Pt(lll) system. J Phys Chem B 109 24-26. 

Examination of the azide bending-mode region (600-700 cm 1) in the SER spectra (Figure 2) is also instructive with regard to adsorbate orientation. Thus, the pair of bands (at ca. 610 and 670 cm"1) seen at the least negative potentials are characteristic of end-on coordinated azide (15) the loss of the lower-frequency partner for E < -0.15 V is therefore also indicative of the removal of azide bound in this adsorbate geometry, again in harmony with the interpretation of the infrared spectra (7). 

Figure 2.12 shows the atomic N 2p orbitals surrounded by atomic Cu 3d orbitals in an ideal, FFH adsorbate geometry where the N atom is located at the same vertical... 

The addition of H2 to chemisorbed C2D2 or C2D4 results in H-D exchange, but no change in the adsorbate geometry is detected by ELS. 

The 2D chiral systems of NN and PVBA do not need a change in local adsorbate geometry in order to show a chiral phase transition [83,86]. Homochiral structures have been observed for PVBA (Fig. 7a) and SDA on Cu(100) [95]. A CW-rotated structure contains exclusively A.-PVBA, while the CCW-rotated structure contains only 5-PVBA (Fig. 29) [86]. Increasing the PVBA coverage above 0.05 molecules per copper atom induces a phase transition into a single achiral structure that possesses two mirror planes (Fig. 29c). Highly resolved STM shows that this structure is now comprised of a <5-/k-PVBA racemate and that the unit cell contains equal numbers of CCW-and CW-rotated units. 

In the present paper we have presented some studies concerning the adsorption of acetylene on copper (100) surfaces, and the adsorption of ethylene on the (100) surfaces of nickel, palladium and platinum. In all these studies we have used a cluster with the same shape and size. Despite the limited size of the clusters used, some very interesting features of the systems adsorbate - metal surfaces were determined, namely adsorbate geometries, adsorption energies and vibrational frequencies. 

Furthermore, because catalysts may undergo restructuring at elevated pressures and temperatures, (14,15,48,51,216,222) or even undergo changes in composition (55,60,252), the availability and nature of adsorption sites and adsorbate geometries at mbar pressures may be different from those existing under UHV, and the most incisive characterizations are those of catalyst under reaction conditions. 

For distances smaller than about 4 A from the surface, decreases for the neutral atom. Once the atom has penetrated the compact surface layer and dislocated some of the adsorbed water molecules, the system is stabilized by pushing the atom towards the surface. The behavior is an example of hydrophobic interactions where the insoluble 1° atom is pushed out of the aqueous phase. As it cannot be pushed into the solid phase, the contact adsorbed geometry is the more favorable arrangement. In order to keep the model simple, for the ion and the atom has been combined with the same ab initio interaction energy obtained for I -Pt9 clusters... 

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