Auto-ionization

Simons J 1989 Modified rotationally adiabatic model for rotational auto ionization of dipole-bound molecular anion J. Chem. Phys. 91 6858-68... 

Auto ionization. Occurs when an internally supraexcited atom or molecular moiety loses an electron spontaneously without further interaction with an energy source. (The state of the atom or molecular moiety is known as a pre-ionization state.)... 

We selected liquid ammonia because of its pronounced solubilizing characteristics and powerful ionizing properties. At -33°C and atmospheric pressure, the pKa-value for auto-ionization of liquid ammonia [2NH3 = NH2 + NH4 ] is 34 and since the equivalent value for water is only 14, many substances (with pKa-values between 14 and 34) which are neutral in water should be capable of splitting off protons in liquid ammonia. Acidic... 

For most of the molecules, the electron flow is from D to A, which is supported by the anti-Aviram-Ratner mechanism of Fig. 11a. However, there may be yet another possibility, shown in Fig. 21 implicit in the analyses of Figs. 9-11 has been the Aviram and Ratner assumption [79] that auto-ionization is a less efficient competing process. If the electric field induces intramolecular ionization first by sufficiently altering the orbital energies, then the direction of electron flow may occur in the anti-AR direction (Fig. 21) ... 

Fig. 21 (a) Rectification in the AR sense electron transfers occur first between electrode MD and the HOMO of the D-o-A molecule (1 ), and between the LUMO and MA (1), thus establishing the zwitterionic excited state D+-a-A , which then (2) relaxes back into the neutral state, (b) Rectification in the anti-AR sense if auto-ionization occurs first (1), forming the excited state D+-a-A by an interaction of the intense electric field and the molecule, followed by transfers to and from the electrodes (2) and (2 ), resulting in the electron passing from MD to MA. The molecular energy levels, which in reality must perforce shift dramatically during the electron transfer process, are drawn here for simplicity as if the molecule were still isolated in the gas phase ... 

Optical spectra of auto ionizing Rydberg states... 

Considering the general equation (1.4) for the auto-ionization of solvent HA, one can define an acid as any substance that will increase [H2A+] and define a base as any substance that will increase [A ] and thus decrease [H2A+]. This definition, which includes both Lewis and Brpnsted s concepts, is used in practice while measuring the acidity of a solution by pH. 

A.K. Bhatia, A. Temkin, J.F. Perkins, Hylleraas variational calculation of auto-ionization states, Phys. Rev. 153 (1967) 177. 

Water is not unique in undergoing auto-ionization. Several other solvents are capable of acting both as acids and bases, e.g., the following equilibrium occurs in liquid ammonia (bp -33°C) ... 

The other application explained here is the ionic product of water, pKw [11], which is essentially the equilibrium constant of the auto-ionization process of water (Kw =... 

Recently, it has been found, that some of the doubly excited levels, are influenced by radiative cascades within the Li-like system. This is especially important for levels with small auto-ionization rates Aa and hence low population due to dielectronic recombination. The temperature dependence is taken into account by corrections to (8.2) [18]. 

There are also a number of non-radiative processes by which the excited (NA, v) states can decay. Auto-ionization and pre-dissociation are the most prominent ones,... 

The pre-dissociation results from a non-adiabatic coupling between electronic states (NA v) and (N A ec) at internuclear distances (usually smaller than the equilibrium distance) that correspond to the vibrational continuum of N A state, or when the N A state is a purely dissociative one. Autoionization and pre-dissociation probabilities for Npa(v) and Npir(v)(N > 4) states have been calculated in [68], while for the states with N < 3 they have been evaluated from experimental measurements [69,70]. Auto-ionization and pre-dissociation rates are very high ( 108s 1 for N = 3,4), and rapidly increase with increasing v. More experimental or theoretical information is needed for these processes. 

The vibrational distribution of H2"(X2X+ v) ions, created by various ionizing (or auto-ionizing) processes of H2(ArA w) discussed in previous two sub-sections, is subject to further redistribution due to collision processes... 

Table A-12. Autoprotolysis constants (auto-ionization ionic products) of some amphiprotic solvents at 25 according to 2 SH = [SH ] [S ] ). 

Incidentally, such plots (Figure 4) may be used to compute approximate values of the bulk dielectric constants of water-organic mixed solvents from the emf measurements provided that the bulk dielectric constant is higher than 40. In fact, for auto-ionizing solvents this may be a convenient method, and our calculations have shown that such computed values are within 5-7% of the experimental values. 

Antimony pentachloride is well known to be a strong Lewis acid, therefore forming adducts with bases B which leads to species BShClj. Auto-ionization may produce ion-pairs of the type B2SbCl4 SbClg in solvents of high dielectric constant. Sb N M R lends itself as a probe for distinguishing the two types of adduct. (170) While the reaction ... 

The adiabatic ionization energy of the anilinide anion is evaluated to be Ilia(PhNII ) = 1.7 0.1 eV, which is smaller than that of 2.25 eV measured for phenolate anion135. TD-DFT computations suggest that the lowest vertical n +- n excitations of the N-anion are centered at 1.9 eV (1 A") and 2.1 eV (l A"). Thus, its excited valence states are expected to be auto-ionizing. Substitution of the H(N) atom by fluorine increases the anion IE by 0.3 eV, whereas substitution by a methyl group slightly reduces it (0.05 eV). 

Since water is amphiprotic, that is, it can act both as an acid and as a base, every aqueous solution is characterized by the auto-ionization process, in which one H2O molecule transfers a proton to another H2O molecule. The water auto-ionization equilibrium must always be satisfied, whether other acids or bases are present in the solution or not. 

Liquid NHj, like water, is an amphiprotic solvent. Write the equation for the auto-ionization of NH3. 

Similar interactions in molecular solutions are characterized by the constant of the intrinsic acid-base auto-ionization, which is the important parameter describing acid-base properties of a solvent. For example, the constant of... 

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