Water dipole model

Fig. 2. Double layer structure water dipole model (44).

The experimental data and arguments by Trassatti [25] show that at the PZC, the water dipole contribution to the potential drop across the interface is relatively small, varying from about 0 V for An to about 0.2 V for In and Cd. For transition metals, values as high as 0.4 V are suggested. The basic idea of water clusters on the electrode surface dissociating as the electric field is increased has also been supported by in situ Fourier transfomr infrared (FTIR) studies [26], and this model also underlies more recent statistical mechanical studies [27]. 

We discuss the rotational dynamics of water molecules in terms of the time correlation functions, Ciit) = (P [cos 0 (it)]) (/ = 1, 2), where Pi is the /th Legendre polynomial, cos 0 (it) = U (0) U (it), u [, Is a unit vector along the water dipole (HOH bisector), and U2 is a unit vector along an OH bond. Infrared spectroscopy probes Ci(it), and deuterium NMR probes According to the Debye model (Brownian rotational motion), both... 

However, these classical models neglect various aspects of the interface, such as image charges, surface polarization, and interactions between the excess charges and the water dipoles. Therefore, the widths of the electrode/electrolyte interfaces are usually underestimated. In addition, the ion distribution within the interfaces is not fixed, which for short times might lead to much stronger electric helds near the electrodes. 

Stern HA, Rittner F, Berne BJ, Friesner RA (2001) Combined fluctuating charge and polarizable dipole models application to a five-site water potential function. J Chem Phys 115(5) 2237-2251... 

Ion-Dipole Model In this model ion-dipole forces are the principal forces in the ion-water interaction. The result of these forces is orientation of water molecules in... 

Figure 4.11. Triple-layer model (Grahame) IHP, inner Helmholtz plane OHP, outer Helmholtz plane (, water dipole +, positive end of the dipole).

The effect of the orientation of water dipoles on the electrode on the properties of the interphase was studied by Macdonald (6) and Mott and Watts-Tobin (7). Bockris et al. (8), in a modification of the Grahame model, considered adsorption of completely hydrated ions at the electrode with the water dipole layer present. 

For the description of a solution of alanine in water two models were compared and combined with one another (79), namely the continuum model approach and the cluster ansatz approach (148,149). In the cluster approach snapshots along a trajectory are harvested and subsequent quantum chemical analysis is carried out. In order to learn more about the structure and the effects of the solvent shell, the molecular dipole moments were computed. To harvest a trajectory and for comparison AIMD (here CPMD) simulations were carried out (79). The calculations contained one alanine molecule dissolved in 60 water molecules. The average dipole moments for alanine and water were derived by means of maximally localized Wannier functions (MLWF) (67-72). For the water molecules different solvent shells were selected according to the three radial pair distributions between water and the functional groups. An overview about the findings is given in Tables II and III. 

The Ion-Dipole Model. In this model ion-dipole forces are the principal forces in the ion-water interaction. The result of these forces is orientation of water molecules in the immediate vicinity of an ion (Fig. 2.11). One end of the water dipole is attached electrostatically to the oppositely charged ion. The result of this orienting force is that a certain number of water molecules in the immediate vicinity of the ion are preferentially oriented, forming a primary hydration shell of oriented water molecules. These water molecules do not move independently in the solution. Rather, the ion and its primary water sheath is a single entity that... 

Fig. 2 A, B. Three layers model of water at the interface with mineral according to Dorst-Hansen164) O = clathrate-like ordering ] = water-dipole. A Vicinal water near non-polar surface. Extensive clathrate-like ordering near interface but minimal disordered region. B Vicinal water near polar surface, disordered region...

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