Extended polarization

Karpfen published a study of trends in halogen bonding between a series of amines and halogens and interhalogens [171]. Iodine-containing electron acceptors were not included. This study involved the use of RHF, MP2, and various DFT methods using extended, polarized basis sets and made extensive use of pulsed-nozzle, FT-microwave spectroscopic data (similar to that... 

For Ag(lOO), the voltammetric curve exhibits two main pairs of peaks and a pair of smaller peaks at lower potentials [265]. The first peak has been ascribed to adsorption, while the second to filling of the remaining sites to a closely packed monolayer and a phase transition. Under conditions of extended polarization, a transformation occurs, similar to that in Ag(lll). However, in contrast to Ag(lll), this transformation relates to... 

Cybulski et al. furnish an example of the sensitivity of the various perturbation components of the H-bond energy to the choice of basis set. In their study of the dimer of HF, 6-3IG refers to a standard split-valence set, with polarization functions. GD is similar in character but was designed to specifically address the dispersion energy more accurately. The S2 set was proposed by Sadlej to produce reliable dipole moments and polarizabilities of the monomers, augmented by extended polarization functions (/on F d on H). Well-... 

The discharge of H on such Raney Ni composite coated electrodes (cf. Ref. 182) is found to be significantly improved by in situ formation of -NifOHjj on those electrodes (182). This effect is due to generation of active Ni sites on reduction of the Ni(OH)j when cathodic Hj evolution takes place. On extended polarization, the electrode becomes slowly deactivated (at 70°C), an effect that may be due to H sorption (183) and/or impurity electrodeposition. 

D Tlads overlayers at low, medium, and high F show internally compressed and rotated hep superstructures with moire pattern as shown in Figs. 3.33 and 3.34 (cf. Section 3.4). The formation of a 2D Me-S surface alloy starts at monatomic steps after extended polarization at relatively high Tor low AE, i.e., between the adsorption peaks A2 and A3 of Figs. 3.53 and 3.54. 

In the system Ag(lll)/Tl H, CIO4, (A , f) measurements were carried out after extended polarization only at high For low AE [3.175, 3.177, 3.178]. The kinetic data were fitted by an empirical equation similar to eq. (3.84) and explained in terms of a site exchange model with localized reactions at the periphery of 2D Meads overlayer clusters only (cf. Fig. 3.57). 

In both studies [3.107, 3.109, 3.175, 3.177, 3.178, 3.330-3.336], the decrease of 9A2(0 of fho adsorption peak A2 with increasing polarization time was used as a measure for the rate of 2D Me-S surface alloy formation. Anodic stripping after extended polarization at A gives additional and direct information on the kinetics of this process. However, such stripping experiments were not systematically carried out. 

Figure 3.63 Influence of monatomic step density, L, on the kinetics of 2D Me-S surface alloy formation in the system Ag(lll)/5 x 10" M Pb(C104)2 + 10 M NaC104 + 5 x 10 M HCIO4 at T = 298 K [3.109]. Pbads coverage in peak A2 decays in desorption experiments after extended polarization at A = 120 mV. Experimental q AE,t) data were interpreted assuming quasi-Nemst behavior (eq.(3.18)) of the system studied. L/cm" 0 (1) < 2 x 10 (2) 1.7 x 10 (3) according to [3.107] (4).

Figure 3.64 Kinetics of 3D Me-S bulk alloy formation in the system Ag(lll)/5 x 10 M CdS04 + 5 X 10 M Na2S04 + 5 x 10 M H2SO4 at T = 298 K [3.102J. Cyclic voltammogram without extended polarization and anodic stripping curves depending on extended polarization at AE = 2 mV Polarization time tp/s = 0 (1) 60 (2) 300 (3) 600 (4) 1200 (5).

A very similar transformation of the original hep adlayer to a surface alloy coverage with the same Tl-Tl interatomic distances and [V3 x V3]R30° symmetry has been observed in the system Tl/Ag(lll) during extended polarization of the incompletely formed first T1 adsorbate layer. As in the system Pb/Ag(lll), there is strong evidence that the transformations proceed from the boundaries of the peripheral adsorbate-free domains inwards on the terraces. However, in contrast to the system Pb/Ag(lll), the transformed coverages include both ordered and disordered domains, and then-desorption results in the formation of monoatomic pits in the substrate with widths of ca. 3 to 10 nm [3]. These pits diminish and finally vanish within a few minutes by coalescence and lateral displacement, at a rate that can be increased markedly by positive shift of the substrate potential. 

Figure 3. Slow adsorbate-substrate rearrangement phenomena after adsorption of incomplete monolayer (peaks A1 + A2) and subsequent extended polarization at constant potential between peaks A2 and A3. STM-images recorded in 0.01 M HCIO4 + 0.005M Pb or Tl. (a) STM image recorded in the system Pb 7Ag(l 11) after 600 s extended polarization. Window size 12 nm grayscale range 0.07 nm. The voltammograms represent the voltammetric behavior before and after 600 s polarization, (b) STM image of the transformed coverage in the system n" /Ag(l 11) after 3000 s extended polarization. Window size...

EPS Extended Polar Selectivity C g with polar characteristics (see also AQ)... 

Many biomolecules are characterized by surfaces containing extended polar regions and also extended non-polar regions. A well-known example is provided by beta-amyloid - the well-known Alzheimer protein. It has extended hydrophobic regions separated by hydrophilic regions, as discussed in Chapter 7. The hydration of extended non-polar planar surfaces may involve novel structures that are orien-tationally inverted relative to clathrate-hke hydration shells, where unsatisfied HBs are directed towards the hydrophobic surface. We have discussed these two geometric arrangements in the appendix to this chapter (Appendix 8.A). 

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