Dynamics of Ions

The dynamics of ion surface scattering at energies exceeding several hundred electronvolts can be described by a series of binary collision approximations (BCAs) in which only the interaction of one energetic particle with a solid atom is considered at a time [25]. This model is reasonable because the interaction time for the collision is short compared witii the period of phonon frequencies in solids, and the interaction distance is shorter tlian the interatomic distances in solids. The BCA simplifies the many-body interactions between a projectile and solid atoms to a series of two-body collisions of the projectile and individual solid atoms. This can be described with results from the well known two-body central force problem [26]. 

Perera, L., Essmann, U., Berkowitz, M. Effect of treatment of long-range forces on the dynamics of ions in aqueous solutions. J. Chem. Phys. 102 (1995) 450-456. 

Among the dynamical properties the ones most frequently studied are the lateral diffusion coefficient for water motion parallel to the interface, re-orientational motion near the interface, and the residence time of water molecules near the interface. Occasionally the single particle dynamics is further analyzed on the basis of the spectral densities of motion. Benjamin studied the dynamics of ion transfer across liquid/liquid interfaces and calculated the parameters of a kinetic model for these processes [10]. Reaction rate constants for electron transfer reactions were also derived for electron transfer reactions [11-19]. More recently, systematic studies were performed concerning water and ion transport through cylindrical pores [20-24] and water mobility in disordered polymers [25,26]. 

This review deals largely with work from my own laboratory. It attempts to show the reader some of the recent developments in the field and the breadth of the scientific questions which are being addressed through investigations of the kinetics and dynamics of ion-molecule reactions as mediated through the presence of bound solvent molecules. 

The explanation for the dichotomy between aromatic nitration versus de-alkylative oxidation in equation (84) lies in the dynamics of ion-radical triad (which is predictably modulated by solvent polarity and added inert salt). For example, the nonpolar dichloromethane favors aromatic nitration via a radical-pair collapse of ArH+, NO, 239 i.e.,... 

In the stepwise case, the intermediate ion radical cleaves in a second step. Adaptation of the Morse curve model to the dynamics of ion radical cleavages, viewed as intramolecular dissociative electron transfers. Besides the prediction of the cleavage rate constants, this adaptation opens the possibility of predicting the rate constants for the reverse reaction (i.e., the reaction of radicals with nucleophiles). The latter is the key step of SrnI chemistry, in which electrons (e.g., electrons from an electrode) may be used as catalysts of a chemical reaction. A final section of the chapter deals... 

William L. Hase, Dynamics of Ion-Molecule Complexes, in Adv. Classical Trajectory Methods, Vol. 2, JAI Press, Greenwich, CT, 1994. 

Recently, detailed molecular pictures of the interfacial structure on the time and distance scales of the ion-crossing event, as well as of ion transfer dynamics, have been provided by Benjamin s molecular dynamics computer simulations [71, 75, 128, 136]. The system studied [71, 75, 136] included 343 water molecules and 108 1,2-dichloroethane molecules, which were separately equilibrated in two liquid slabs, and then brought into contact to form a box about 4 nm long and of cross-section 2.17 nmx2.17 nm. In a previous study [128], the dynamics of ion transfer were studied in a system including 256 polar and 256 nonpolar diatomic molecules. Solvent-solvent and ion-solvent interactions were described with standard potential functions, comprising coulombic and Lennard-Jones 6-12 pairwise potentials for electrostatic and nonbonded interactions, respectively. While in the first study [128] the intramolecular bond vibration of both polar and nonpolar solvent molecules was modeled as a harmonic oscillator, the next studies [71,75,136] used a more advanced model [137] for water and a four-atom model, with a united atom for each of two... 

The results of investigating the dynamics of ion exchange (see Sec. VI) show that the lowest value of HETP or HTU is obtained by exchange of ions in a dense bed. When the bed is less densely packed column efficiency is decreased. 

In the last decades the overwhelming majority of the experimental studies of the structure and dynamics of ions targeted the aqueous solutions and the water itself, and less attention has been paid to other solvents and non-aqueous solutions. Theoreticians and traditional (e.g. IR, Raman, NMR) showed more interest to non-aqueous systems, but the predominance of aqueous solutions is still well reflected in the reviews [1]. 

I. Benjamin, Mechanism and dynamics of ion transfer across a liquid-liquid interface. Science 261 (1993) 1558. 

A.I.Maergoiz, E.E.Nikitin and L.Yu.Rusin, Dynamics of ion formation in collision-induced dissociation of diatomic molecules, in Khimiya Plasiiiy 11, ed. B. M. Smirnov, Moscow, Atomizdat, 1985, p. 3... 

Considerably more studies consider solute behaviour at the liquid/liquid and liquid/vapor interfaces. Molecular mechanism and dynamics of ion transfer... 

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