Water ionization potential

The setup for atmospheric pressure photoionization (APPI) (Bos et ah, 2006 Hanold et ah, 2004 Raffaelli and Saba, 2003 Robb et ah, 2000) is very similar to that of APCI (Fig. 8.7). Only the corona discharge is replaced by a gas discharge lamp (krypton,10.0 eV) that generates ultraviolet (UV) photons in vacuum. The liquid phase is also vaporized by a pneumatic nebulizer and different geometries are used. Most analytes have ionization potentials below 10 eV, while high-pressure liquid chromatography (HPLC) solvents have higher ionization potentials (water 12.6 eV, methanol 10.8 eV, and acetonitrile 12.2 eV). 

Reactions in Water. The ionization potential for bromine is 11.8 eV and the electron affinity is 3.78 eV. The heat of dissociation of the Br2 molecule is 192 kj (46 kcal). The reduction potentials for bromine and oxybromide anions in aqueous acid solutions at 25°C are (21) ... 

A mixture of water/pyridine appears to be the solvent of choice to aid carbenium ion formation [246]. In the Hofer-Moest reaction the formation of alcohols is optimized by adding alkali bicarbonates, sulfates [39] or perchlorates. In methanol solution the presence of a small amount of sodium perchlorate shifts the decarboxylation totally to the carbenium ion pathway [31]. The structure of the carboxylate can also support non-Kolbe electrolysis. By comparing the products of the electrolysis of different carboxylates with the ionization potentials of the corresponding radicals one can draw the conclusion that alkyl radicals with gas phase ionization potentials smaller than 8 e V should be oxidized to carbenium ions [8 c] in the course of Kolbe electrolysis. This gives some indication in which cases preferential carbenium ion formation or radical dimerization is to be expected. Thus a-alkyl, cycloalkyl [, ... 

For cationic zeolites Richardson (79) has demonstrated that the radical concentration is a function of the electron affinity of the exchangeable cation and the ionization potential of the hydrocarbon, provided the size of the molecule does not prevent entrance into the zeolite. In a study made on mixed cationic zeolites, such as MgCuY, Richardson used the ability of zeolites to form radicals as a measure of the polarizing effect of one metal cation upon another. He subsequently developed a theory for the catalytic activity of these materials based upon this polarizing ability of various cations. It should be pointed out that infrared and ESR evidence indicate that this same polarizing ability is effective in hydrolyzing water to form acidic sites in cationic zeolites (80, 81). 

As we have recently shown [3], the stability of GIC with Bronstcd acids is governed by ionization potential of the intercalated anion. Solvation of the anion substantially increases ionization potential and hence stabilizes GIC. Such a possibility was predicted by Inagaki [4] who proposed to use organic molecules as additional cointercalants for the purpose of stabilization. Afterwards, we successfully used glacial acetic acid and water to synthesize stable products [5],... 

In Sect. 4.9.1, experimental rationalization was provided for the W value of ionization in gaseous and liquid water, giving respectively 30.0 and 20.8 eV. The corresponding ionization potentials are respectively 12.6 and 8.3 eV. For the purpose of diffusion and stochastic kinetics, one often requires the statistical distribution P(i,j) of the number of ionizations i and excitations j, conditioned on i ionizations, for a spur of energy . Pimblott and Mozumder (1991) write P(i, j) = r(i) 2(j i), where F(i) is the probability of having i ionizations and 2(j i) is the probability of having j excitations conditioned on i ionizations. These probabilities are separately normalized to unity. 

Pimblott and Mozumder (1991) used Eq. (4.26) for both gaseous and liquid water, utilizing experimental information on ionization potentials, W values, ionization efficiencies, and the relevant cross sections. Their findings are briefly summarized as follows ... 

Following Platzman (1967), Magee and Mozumder (1973) estimate the total ionization yield in water vapor as 3.48. The yield of superexcited states that do not autoionize in the gas phase is 0.92. Assuming that all of these did autoion-ize in the liquid, we would get 4.4 as the total ionization yield. This figure is within the experimental limits of eh yield at 100 ps, but it is less than the total experimental ionization yield by about 1. The assumption of lower ionization potential in the liquid does not remove this difficulty, as the total yield of excited states in the gas phase below the ionization limit is only 0.54. 

The one-electron oxidation of iV-benzylphenothiazine by nitric acid occurs in the presence of /i-cyclodextrin, which stabilizes the radical cation by incorporation into its cavity. The reaction is inhibited by adamantane, which preferentially occupies the cavity. Novel Pummerer-type rearrangements of / -sulfinylphenyl derivatives, yielding /7-quinones and protected dihydroquinones, and highly enantioselective Pummerer-type rearrangements of chiral, non-racemic sulfoxides have been reviewed. A comprehensive study has demonstrated that the redox potential for 7- and 8-substituted flavins is linearly correlated with Hammett a values. DFT calculations in [3.3.n]pro-pellanes highlight low ionization potentials that favour SET oxidative cleavage of the strained central C-C bond rather than direct C-H or C-C bond attack. Oxidations and reductions in water have been reviewed. ... 

Since the publication of the third edition, additional data have been critically reviewed. New or additional data included in this edition are bioconcentration factors, aquatic mammalian toxicity values, degradation rates, corresponding half-lives in various environmental compartments, ionization potentials, aqueous solubility of miscellaneous compounds, Henry s law constants, biological, chemical, and theoretical oxygen demand values for various organic compounds. Five additional tables have been added Test Method Number Index, Dielectric Values of Earth Materials and Fluids, Lowest Odor Threshold Concentrations of Organic Compoimds in Water, and Lowest Threshold Concentrations of Organic Compounds in Water. 

To prevent misunderstanding (94), we emphasize that neither experimental hydration energies nor experimental coordination numbers are necessary for these calculations. Moreover, the coordination numbers obtained are generally not comparable to empirical hydration numbers. The only experimental quantities that enter the calculations are a) cationic radius and charge b) van der Waals radius of water c) dipole and quadrupole moment of water d) polarizabilities e) ionization potentials and f) Born repulsion exponents as well as fundamental constants (see Ref. (92)). 

This section is about diaUcylethers, aldehydes, ketones and alcohols. Oxygen net charges deduced from standard STO-3G calculations are indicated in Table 6.7 (see also Fig. 6.9), along with their NMR shifts (ppm from water) for dialkylethers [140] and carbonyl compounds [140], as well as selected ionization potentials [147]. 

The kineties of eleetron-transfer reactions, which is also affected by the electrode potential and the metal-water interface, is more difficult and complex to treat than the thermodynamic aspects. While the theoretical development for electron transfer kinetics began decades ago, a practical implementation for surface reactions is still unavailable. Popular transition state-searching techniques such as the NEB method are not designed to search for minimum-energy reaction paths subject to a constant potential. Approximations that allow affordable quantum chemistry calculations to get around this limitation have been proposed, ranging from the electron affinity/ionization potential matching method to heuristic arguments based on interpolations. 

The ionization potentials of some of the bipyridines have been investigated. Solubility data for 2,2 -bipyridine in aqueous solution, in aqueous solvent mixtures, and in various aqueous salt solutions have been obtained, whereas the heat of solution, heat capacities, and related data for 2,2 - and 4,4 -bipyridines in water have been measured. The enthalpies of solution of 2,2 -bipyridine in water and aqueous solvent mixtures have also been obtained. Dielectric relaxation studies of 2,2 -bipyri-dine in carbon tetrachloride have been reported in connection with hindered internal rotation. Partition coefficients for 2,2 -bipyridine between water and various organic solvents have been measured. ... 

The above considerations need relativistic correction at v c, which may be performed in a straightforward manner. More importantly, Eq. (10) assumes that the ionization process is direct, i.e., once a state above the ionization potential is reached, ionization occurs with a certainty. Platzman [25] points out that in molecules, this is not necessarily so and superexcited states with energy exceeding the ionization potential may exist, which will dissociate into neutral fragments with a certain probability. For example, in water in the gas phase, ionization occurs with a sharp threshold at the ionization potential (I.P.) = 12.6 eV, but only with an efficiency of 0.4. Beyond the I.P., the ionization... 

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