Ion/molecule interaction and

However, SEDI fails to account for attractive ion-molecule interactions and thus suffers from same handicaps as EHSS (1.4.3)— inaccuracy of absolute mobihties and inability to predict K(J) or K(E) dependences. The best features of SEDI and TC are combined in the SEDl-TC hybrid, which assumes repulsive and attractive interactions to be mutually independent such that O for ions A and B are related by... 

For the ion-molecule Interactions and molecule self Interactions, Pitzer and Silvester were able to determine the X and p terms. The following equations... 

Intramolecular Isotope Effects. The data in Figure 2 clearly illustrate the failure of the experimental results in following the predicted velocity dependence of the Langevin cross-section. The remark has been frequently made that in the reactions of complex ions with molecules, hydrocarbon systems etc., experimental cross-sections correlate better with an E l than E 112 dependence on reactant ion kinetic energy (14, 24). This energy dependence of reaction presents a fundamental problem with respect to the nature of the ion-molecule interaction potential. So far no theory has been proposed which quantitatively predicts the E l dependence, and under these circumstances interpreting the experiment in these terms is questionable. 

Studies with the high pressure ion source can be divided into two classes ion-molecule reactions and ion-dipole molecule interactions. Previous work (20, 21) dealing with the ion-molecule reactions will be considered in this text where it relates to the new results. The study of ion-dipole (solvent) molecule interactions (14, 15, 22) is not considered part of this paper. 

Lowering the temperature has a similar effect on the deuterium spectra as does increased loadings. In Figure 3, spectra for benzene-d6/(Na)X at 0.7 molecules/supercage over the temperature range 298 to 133 K are shown. It is observed that both benzene species are detected simultaneously between 228 and 188 K. Below this temperature the oriented benzene species becomes the predominant form. A similar situation occurs for polycrystalline benzene-dg in which two quadrupole patterns, one static and the other motionally narrowed due to C rotation, are observed to coexist at temperatures between 110 and 130 K (7). This behavior has been attributed to sample imperfections (8) which give rise to a narrow distribution in correlation times for reorientation about the hexad axis. For benzene in (Na)X and (Cs,Na)X such imperfections may result from the ion/benzene interaction, and a nonuniform distribution of benzene molecules and ions within the zeolite. These factors may also be responsible for producing the individual species. However, from the NMR spectra it is not possible to... 

The thermodynamic properties of a mixture depend on the forces which operate between the species of the mixture. Electrolyte systems are characterized by the presence of both molecular species and ionic species, resulting in three different types of interaction. They are ion-ion interaction, molecule-molecule interaction, and ion-molecule interaction. 

Recently, the Pitzer equation has been applied to model weak electrolyte systems by Beutier and Renon ( ) and Edwards, et al. (10). Beutier and Renon used a simplified Pitzer equation for the ion-ion interaction contribution, applied Debye-McAulay s electrostatic theory (Harned and Owen, (14)) for the ion-molecule interaction contribution, and adoptee) Margules type terms for molecule-molecule interactions between the same molecular solutes. Edwards, et al. applied the Pitzer equation directly, without defining any new terms, for all interactions (ion-ion, ion-molecule, and molecule-molecule) while neglecting all ternary parameters. Bromley s (1) ideas on additivity of interaction parameters of individual ions and correlation between individual ion and partial molar entropy of ions at infinite dilution were adopted in both studies. In addition, they both neglected contributions from interactions among ions of the same sign. 

In order to gain deeper insight into the nature of ion-molecule interactions it is necessary to rely upon quantum mechanics. Thereby we can obtain, at least in principle, a description of the observable phenomena (including those nonacces-sible by classical theories) which is precise and free of parameters. In recent years considerable interest has evolved in calculations of this type. 

The ion-water interactions are very strong Coulomb forces. As the hydrated ion approaches the solution/metal interface, the ion could be adsorbed on the metal surface. This adsorption may be accompanied by a partial loss of coordination shell water molecules, or the ion could keep its coordination shell upon adsorption. The behavior will be determined by the competition between the ion-water interactions and the ion-metal interactions. In some cases, a partial eharge transfer between the ion and the metal results in a strong bond, and we term this process chemisorption, in contrast to physisorption, which is much weaker and does not result in substantial modification of the ion s electronic structure. In some cases, one of the coordination shell molecules may be an adsorbed water molecule. hi this case, the ion does not lose part of the coordination shell, but some reorganization of the coordination shell molecules may occur in order to satisfy the constraint imposed by the metal surface, especially when it is charged. 

Phase, (NATO Advanced Study Institute on Ion Molecule Interactions), Interaction Between Ions and Molecules, Plenum Press, New York, 1975. 

Several books and review chapters devoted to the field of ion-neutral reactions in the gas phase have appeared in recent years, la 8, j,k some of which are concerned at least in part with the special topic of interest for the present review chapter—namely, the role of excited states in such interactions. The present review attempts to present a comprehensive survey of the latter subject, and the processes to be discussed include those in which an excited ion interacts with a ground-state neutral, interaction of an excited neutral with a ground-state ion, and on-neutral interactions that produce excited ionic products or excited neutral products. Reactions in which ions are produced by reaction of an excited neutral species with another neutral, for example, Penning ionization, are not included in the present chapter. For a recent review of this topic, the reader is referred to the article by Rundel and Stebbings.1 Electron-molecule interactions and photon-molecule interactions are discussed here only as they relate to the production of ions in excited states, which can then be reacted with neutral species. 

Recent advances in experimental techniques, particularly photoionization methods, have made it relatively easy to prepare reactant ions in well-defined states of internal excitation (electronic, vibrational, and even rotational). This has made possible extensive studies of the effects of internal energy on the cross sections of ion-neutral interactions, which have contributed significantly to our understanding of the general areas of reaction kinetics and dynamics. Other important theoretical implications derive from investigations of the role of internally excited states in ion-neutral processes, such as the effect of electronically excited states in nonadiabatic transitions between two potential-energy surfaces for the simplest ion-molecule interaction, H+(H2,H)H2+, which has been discussed by Preston and Tully.2 This role has no counterpart in analogous neutral-neutral interactions. 

Statistical theories treat the decomposition of the reaction complex of ion-molecule interactions in an analogous manner to that employed for unimolecular decomposition reactions.466 One approach is that taken by the quasiequilibrium theory (QET).467 Its basic assumptions are (1) the rate of dissociation of the ion is slow relative to the rate of redistribution of energy among the internal degrees of freedom, both electronic and vibrational, of the ion and (2) each dissociation process may be described as a motion along a reaction coordinate separable from all other internal... 

The topic of interactions between Lewis acids and bases could benefit from systematic ab initio quantum chemical calculations of gas phase (two molecule) studies, for which there is a substantial body of experimental data available for comparison. Similar computations could be carried out in the presence of a dielectric medium. In addition, assemblages of molecules, for example a test acid in the presence of many solvent molecules, could be carried out with semiempirical quantum mechanics using, for example, a commercial package. This type of neutral molecule interaction study could then be enlarged in scope to determine the effects of ion-molecule interactions by way of quantum mechanical computations in a dielectric medium in solutions of low ionic strength. This approach could bring considerable order and a more convincing picture of Lewis acid base theory than the mixed spectroscopic (molecular) parameters in interactive media and the purely macroscopic (thermodynamic and kinetic) parameters in different and varied media or perturbation theory applied to the semiempirical molecular orbital or valence bond approach [11 and references therein]. 

The addition of polar molecules to electrolyte solutions effects a much larger change in conductance if low dielectric solvents are employed In a series of papers Gilkerson et a/. studied the ion-molecule interaction of tertiary and quarternary ammonium cations with Lewis bases in low dielectric solvents, like o-dichlorobenzene, chlorobenzene or 1,2-dichloroethane. The change of the ion-pair association constant with concentration of an additive L was attributed to the formation of 1 1 cation-molecule complexes ... 

Within the last 5 years a number of quantum mechanical calculations have been carried out, in particular for hydrogen-bonded systems such as HgO, NHg, and HF as solvents. Contrary to electrostatic models, MO calculations allow for the possibility of covalent bond formation and, consequently, constitute a fundamentally better approach to ion-molecule interactions. Some interesting results of recent model calculations, although qualitative in nature, are discussed in Section V. 

If the electric field is caused by an ion, then E = qi/R y where q is the ionic change, i is the unit vector along the ion-molecule direction, and R the ion-molecule distance, which is the E =-l/2aq /R for this ion-induced dipole interaction. The correspondingformulafor dli-pole-induced dipole interaction between two dipolar molecules is... 

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