Double dissociation of water

Table 3. The f em symmetric double dissociation of water (into 2H(ls 2S) + 0(2p4 3P) cut (ii)). The H-O-H angle is kept fixed at its equilibrium value taken from Ref. [139] (ae = 104.501 degree). R is an O-H distance and Re = 0.95785 A is the equilibrium value of R [139]. All energies E (in cm-1) are reported as E - E(Re, ae), where E(Re, ae) are the corresponding values of E at the equilibrium geometry. X is a cardinal number defining the aug-cc-pCVXZ basis sets used in the calculations. In all CC calculations, all electrons were correlated.

Figure 11.44 is a schematic diagram of one LIF instrument (Stevens et al., 1994 Brune et al., 1998). An air-cooled copper-vapor laser pumps a dye laser whose output at 616 nm is doubled to generate the 308-nm exciting radiation. An OH reference cell in which OH is generated from the thermal dissociation of water... 

As you know, all aqueous solutions contain ions. Even pure water contains a few ions that are produced by the dissociation of water molecules. Remember The double arrow in the equation shows that the reaction is reversible. The ions recombine to form water molecules. 

At the pristine water-water vapour Interface spontaneous polarization of the water molecules takes place, leading to the fpotentIal. Prlstlnlty implies that there are no other ions or dissolved molecules apart from minute amounts of H and OH Ions, created by spontaneous dissociation of water molecules and which may give rise to a weak superimposed Ionic double layer. There Is no operational procedure to establish this f-potentlal but present-day consensus has It that the alr-slde Is negative, see sec. 3.9. At Issue Is now the formation of ionic double layers in addition to this when the solution contains simple electrolytes. The more dramatic changes caused by adsorbed or spread surfactants will not be addressed here. 

An often applied procedure for mechanically stabilizing bubbles is to rotate them in cylindrical tubes towards the centre, Quincke applied this idea as long ago as 1861. Kelsall et reviewed this matter and added their own measurements, mostly in the presence of electrolytes. Intentionally added electrol)des obviously swamp the H and OH ions stemming from the intrinsic dissociation of water. Kellsall et al. used a double laser-Doppler apparatus by which the difference between the bubble rise velocity with and without the applied field could be measured. They found the mobility to depend on size and pH, but it could at least be... 

From y(ln c) plots the surface concentration F can be obtained and from these the surface chcirge a°, assuming complete dissociation. We already presented results in fig. II.3.76 which demonstrated that a° =0(1-5 pC/cm ), exceeding the contribution by the Intrinsic dissociation of water to the double layer by a factor of 102. 

The high degree of self-dissociation of water at high densities leads to catalysis of water elimination from alcohols and the formation of double bonds. In the case of tert-butanol [25], complete conversion to isobutene is achieved in 30 s at subcritical temperatures without addition of acids. In other cases, such as the elimination of water from ethanol [26], propanol [27, 28], glycerol [29], glycol [30], fructose [31,... 

The results for the dissociation of water at the metal/solution interface show the well-known double-layer structure that is at the heart of most electrochemical systems. While the negative charge is delocalized, it still acts to polarize the surface. The proton which forms exists as either a hydronium (H3O+) or a Zundel (H5O2 ) ion both of which are about one solvation shell removed from the surface. This is known as the inner-layer Helmholtz layer. The chemistry that occurs at the interface polarizes the surface, which ultimately leads to a potential across the interface. In an actual system, the electrolyte plays an important role in establishing the potential as well as in potentially altering the structure and chemistry that occur at the interface. 

The overall description of the double dissociation of the water molecule by the QMMCC(2,6) method is almost perfect. Indeed, the QMMCC(2,6) approach reduces the 1.790, 5.590, and 9.333 millihartree errors in the CCSD results at i = i e 1.5i e, and 2i2e, respectively, to less than 0.7 millihartree in the entire R = Re — 2Re region. As in all other examples discussed in this section, those remarkable improvements are accomplished by adding the a posteriori noniterative corrections, employing the CCSD values of the Ti and T2 components, to CCSD energies. Interestingly enough. 

In the system of desalted water-air, when water doesn t contain any surfactants, the double electric layer at the air bubble surface is formed due to the structure and charge distribution in water molecules and due to the presence of charged hydroxyls and protons arisen as a result of dissociation of water molecules. In order to estimate the maximum charge density at the bubbles owing to water molecule dissociation, let s use the expression for the dissociation constant of water in its bulk and at the interface, respectively ... 

The H entry into a metal fiom an aqueous electrolyte is believed to involve the same surface-bulk transfer step as in the gas phase, but the preliminary adsorption step is a more complex process because more H sources are involved in aqueous solution, allowing more possible H surface reactions, and also because of the specificity of the electrolyte-metal interface. Whereas H adsorption in the gas phase occurs by dissociative adsorption of gaseous H2 on the free sites of a bare metallic surface, H adsorption in aqueous solution may occur either chemically by dissociation of dissolved H2 or electrochemically from solvated (hydrated) protons or water molecules it takes place on a hydrated surface and thus implies the displacement of adsorbed water molecules or specifically adsorbed ions and local reorganization of the double layer [20] competition with the adsorption of oxygen species formed from the dissociation of water may also occur [21-23], The adsorbed H layer is also in interaction with surrounding water molecules, i.e., it is hydrated [8c,24,25],... 

FIG. 9 Schematic illustration of adsorption of poly(styrenesulfonate) on an oppositely charged surface. For an amphiphile surface in pure water or in simple electrolyte solutions, dissociation of charged groups leads to buildup of a classical double layer, (a) In the initial stage of adsorption, the polymer forms stoichiometric ion pairs and the layer becomes electroneutral, (b) At higher polyion concentrations, a process of restructuring of the adsorbed polymer builds a new double layer by additional binding of the polymer. 

Althongh van der Waals forces are present in every system, they dominate the disjoining pressnre in only a few simple cases, such as interactions of nonpolar and inert atoms and molecnles. It is common for surfaces to be charged, particularly when exposed to water or a liquid with a high dielectric constant, due to the dissociation of surface ionic groups or adsorption of ions from solution, hi these cases, repulsive double-layer forces originating from electrostatic and entropic interactions may dominate the disjoining pressure. These forces decay exponentially [5,6] ... 

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