Simple Ionic Species Research Articles

Fluids of the Lower Crust: Deep Is Different

Deep fluids are important for the evolution and properties of the lower continental and arc crust in tectonically active settings. They comprise four components: H2O, nonpolar gases, salts, and rock-derived solutes. Contrasting behavior of H2O-gas and H2O-salt mixtures yields immiscibility and potential separation of phases with different chemical properties. Equilibrium thermodynamic modeling of fluid-rock interaction using simple ionic species known from shallow-crustal systems yields solutions too dilute to be consistent with experiments and resistivity surveys, especially if CO2is added. Therefore, additional species must be present, and H2O-salt solutions likely explain much of the evidence for fluid action in high-pressure settings. At low salinity, H2O-rich fluids are powerful solvents for aluminosilicate rock components that are dissolved as polymerized clusters. Addition of salts changes solubility patterns, but aluminosilicate contents may remain high. Fluids with Xsalt= 0.05 to 0.4 in equilibrium with model crustal rocks have bulk conductivities of 10−1.5to 100 S/m at porosity of 0.001. Such fluids are consistent with observed conductivity anomalies and are capable of the mass transfer seen in metamorphic rocks exhumed from the lower crust.

Molecular Dications in Planetary Atmospheric Escape

Fundamental properties of multiply charged molecular ions, such as energetics, structure, stability, lifetime and fragmentation dynamics, are relevant to understand and model the behavior of gaseous plasmas as well as ionosphere and astrophysical environments. Experimental determinations of the Kinetic Energy Released (KER) for ions originating from dissociations reactions, induced by Coulomb explosion of doubly charged molecular ions (molecular dications) produced by double photoionization of CO2, N2O and C2H2 molecules of interest in planetary atmospheres, are reported. The KER measurement as a function of the ultraviolet (UV) photon energy in the range of 28–65 eV was extracted from the electron-ion-ion coincidence spectra obtained by using tunable synchrotron radiation coupled with ion imaging techniques at the ELETTRA Synchrotron Light Laboratory Trieste, Italy. These experiments, coupled with a computational analysis based on a Monte Carlo trajectory simulation, allow assessing the probability of escape for simple ionic species in the upper atmosphere of Mars, Venus and Titan. The measured KER in the case of H+, C+, CH+, CH2+, N+, O+, CO+, N2+ and NO+ fragment ions range between 1.0 and 5.5 eV, being large enough to allow these ionic species to participate in the atmospheric escape from such planets into space. In the case of Mars, we suggest a possible explanation for the observed behavior of the O+ and CO22+ ion density profiles.

The Possible Role of Penning Ionization Processes in Planetary Atmospheres

In this paper we suggest Penning ionization as an important route of formation for ionic species in upper planetary atmospheres. Our goal is to provide relevant tools to researchers working on kinetic models of atmospheric interest, in order to include Penning ionizations in their calculations as fast processes promoting reactions that cannot be neglected. Ions are extremely important for the transmission of radio and satellite signals, and they govern the chemistry of planetary ionospheres. Molecular ions have also been detected in comet tails. In this paper recent experimental results concerning production of simple ionic species of atmospheric interest are presented and discussed. Such results concern the formation of free ions in collisional ionization of H2O, H2S, and NH3 induced by highly excited species (Penning ionization) as metastable noble gas atoms. The effect of Penning ionization still has not been considered in the modeling of terrestrial and extraterrestrial objects so far, even, though metastable helium is formed by radiative recombination of He+ ions with electrons. Because helium is the second most abundant element of the universe, Penning ionization of atomic or molecular species by He*(23S1) is plausibly an active route of ionization in relatively dense environments exposed to cosmic rays.

Ion-regulated allosteric binding of fullerenes (C60 and C70) by tetrathiafulvalene-calix[4]pyrroles.

The effect of ionic species on the binding of fullerenes (C60 and C70) by tetrathiafulvalene-calix[4]pyrrole (TTF-C4P) receptors and the nature of the resulting supramolecular complexes (TTF-C4P + fullerene + halide anion + tetraalkylammonium cation) was studied in the solid state through single crystal X-ray diffraction methods and in dichloromethane solution by means of continuous variation plots and UV-vis spectroscopic titrations. These analyses revealed a 1:1 stoichiometry between the anion-bound TTF-C4Ps and the complexed fullerenes. The latter guests are bound within the bowl-like cup of the C4P in a ball-and-socket binding mode. The interactions between the TTF-C4P receptors and the fullerene guests are highly influenced by both the nature of halide anions and their counter tetraalkylammonium cations. Three halides (F(-), Cl(-), and Br(-)) were studied. All three potentiate the binding of the two test fullerenes by inducing a conformational change from the 1,3-alternate to the cone conformer of the TTF-C4Ps, thus acting as positive heterotropic allosteric effectors. For a particular halide anion, the choice of tetraalkylammonium salts serves to modulate the strength of the TTF-C4P-fullerene host-guest binding interactions and, in conjunction with variations in the halide anion, can be exploited to alter the inherent selectivity of the host for a given fullerene. Differences in binding are reflected in the excited state optical properties. Overall, the present four-component system provides an illustration of how host-guest binding events involving appropriately designed artificial receptors can be fine-tuned via the addition of simple ionic species as allosteric modulators.

Kinetic Energy Release in molecular dications fragmentation after VUV and EUV ionization and escape from planetary atmospheres

The measurements of the Kinetic Energy Release (KER) for various ionic species originating from two-body dissociations reactions, induced by double photoionization of CO2, C2H2 and N2O neutral molecular precursors of interest in planetary atmospheres, are reported. The KER distributions as a function of the ultraviolet (UV) photon energy in the range of 30–65eV (Vacuum and Extreme UV photons) are extracted from the electron–ion–ion coincidence spectra obtained by using tunable synchrotron radiation coupled with ion imaging techniques. This experimental method allows assessing the probability of escape for some simple ionic species in the upper atmosphere of Mars and Titan. In fact, the KER measured for H+, C+, CH+, CH2+, N+, O+, CO+, N2+ and NO+ fragment ions are ranging between 1.0 and 5.5eV (only for H+ the maximum value reaches 6.0eV), and these translational energies are large enough to allow these ionic species in participating in the atmospheric escape from Mars and Titan into space (for CO+, N2+ and NO+, the measured KER of 0.5–2.5eV, 0.5–2.8eV and 1.0–2.5eV, respectively, allows the possible escape only from the Titan atmosphere).

Electrical Conductivity of Mixed Electrolytes: Modeling within the Mean Spherical Approximation

The purpose of this study is to predict the electrical conductivity of an electrolyte solution containing several simple ionic species. Explicit equations of the MSA-transport theory for the electrical conductivity in this complex solution are given. The theoretical conductivity of simple salts is first compared to experimental results of the literature to deduce the sizes of the ions. These sizes allow us to calculate the conductivity for a mixture of several ionic species without any additional parameter. We have also measured the electrical conductivity of solutions of LiCl, NaCl, and KCl and of KBr and MgCl(2) at 25 degrees C. A very good agreement between theoretical calculations and experimental values is obtained for each studied system.

The electrochemistry of Pb II activated sphalerite in relation to flotation

Fine sphalerite was pressed into a thermosetting graphitic polymer matrix and a reusable electrode suitable for dynamic electrochemical measurements was obtained. After activation of the sphalerite by Pb II, cyclic voltammetry was performed in the absence and presence of potassium ethyl xanthate. The resultant anodic and cathodic waves were compared with voltammograms obtained from the literature, ‘stripping’ analysis of a graphitic electrode, as well as with the behaviour of galena and Cu II activated sphalerite electrodes. This work suggests that adsorbed Pb II on sphalerite is present as a simple ionic species, behaving similarly to Pb(OH) 2 during reduction and reacting with ethyl xanthate by ion exchange.

Effect of Geometric Constraints on the Self-Assembled Monolayer Formation of Aromatic Disulfides on Polycrystalline Gold

The self-assembled monolayer (SAM) formation tendency of two comparatively small aromatic disulfide molecules, namely naphthalene disulfide (NDS) and diphenyl disulfide (DDS), has been investigated using quartz crystal microgravimetry (QCM), cyclic voltammetric, and impedance techniques. The typical time period for monolayer formation on polycrystalline gold has been found to be about 2 h for both the molecules from the QCM data. A significant change in double-layer capacitance values (from 21 μF/cm2 for bare gold to ∼14 and ∼8 μF/cm2 for NDS and DDS, respectively) upon monolayer formation for both the cases has been observed, which correlates well with the QCM area per molecule values (∼49 and 36 Å2 for NDS and DDS, respectively). The difference in the permeability of the two monolayers to simple ionic species was also investigated using K3Fe(CN)6 as redox probes in aqueous solution. A mixed linear/radial mode of diffusion is observed at the DDS-modified electrode in contrast to a predominant linear one at the electrode derivatized with a NDS monolayer. Impedance measurements indicate apparent surface coverages of 99.6 and 99.8% and rate constants of 9.4 × 10-5 and 4.1 × 10-5 cm/s for the Fe(CN)63-/4- couple in the case of NDS and DDS, respectively. These results strongly demonstrate the effect of geometrical constraints in controlling the microscopic structure and the packing density of the SAMs and highlight the importance of intramolecular conformational changes in controlling the monolayer packing density.

Model for the Conductivity of Ionic Mixtures in the Mean Spherical Approximation. 2. Surfactant Solutions

We recently obtained analytic expressions for the concentration dependence of the conductance of a mixture with three simple ionic species. These expressions are available at concentrations up to 1...

New perspectives in the transport of electrolyte solutions

Abstract

Model for the Conductivity of Ionic Mixtures within the Mean Spherical Approximation. 1. Three Simple Ionic Species

We recently obtained simple expressions for the concentration dependence of the conductance of an electrolyte with two simple species and a mixture with three ionic species. The Fuoss−Onsager continuity equations were solved using equilibrium pair distribution functions. Various equilibrium pair correlation functions can be used for this purpose; those of the MSA theory (mean spherical approximation) yield explicit expressions for the variation of conductivity with concentration, which are in good agreement with the experimental data. Aqueous solutions of NaCl, KCl, and MgCl2 and mixtures of NaCl/KCl and NaCl/MgCl2 were examined at concentrations up to 1 equiv of solute per liter.

An X-ray crystallorgraphic study of the reagent Ph3PCl2; not charge-transfer, R3P–Cl–Cl, trigonal bipyramidal or [R3PCl]Cl but an unusual dinuclear ionic species, [Ph3PCl+⋯Cl–⋯+CIPPH3]Cl containing long Cl–Cl contacts

An X-ray crystallographic study of the reagent Ph3PCl2 reveals it to be [Ph3PCl+⋯Cl–⋯+ClPPh3]Cl and not trigonal bipyramidal, molecular charge-transfer Ph3P–Cl–Cl or the simple ionic species [Ph3PCl]Cl; this contrasts with the conclusions from all previous spectroscopic data recorded on compounds of stoichiometry R3PCl2 by earlier workers, and represents the first compound of this formula to be crystallographically characterised.

Structure and Dynamics in Calcium Aluminate Liquids: High‐Temperature 27Al NMR and Raman Spectroscopy

27Al NMR spectra of CaO–Al2O3 liquids at 2500 K have been obtained using a recently developed technique that involves CO2 laser heating and sample levitation inside the NMR magnet. The spectra consist of single, narrow lines (100 to 200 Hz FWHM), indicating that rapid chemical exchange among molecular species occurs in the liquids. Isotropic chemical shifts vary linearly with composition, becoming more shielded with increasing Al2O3content. This is most likely due to an increase in the average nearest‐neighbor coordination of Al, as the proportion of higher coordinate Al species (AlO5 and AlO6) has been observed to increase with alumina content in glasses along this join. This is also in agreement with ion dynamics simulations of liquids along the CaO–Al2O3 join, which show the average Al coordination to range from 4 at low alumina content to 5 for Al2O3liquid. Correlation times for 27Al spin–lattice relaxation estimated from the NMR line widths are in agreement with shear relaxation times determined from experimental viscosity measurements. This may indicate that oxygen exchange between neighboring aluminate polyhedra is a key component in the mechanism for viscous flow. Viscosities determined from oxygen ion diffusion coefficients via ion dynamics simulation agree well with extrapolation of experimental data, in further support of this. We have also obtained high‐temperature Raman spectra of CaAl2O4 and Ca12Al14O33 glasses and liquids up to 1928 K. The liquid spectra contain structure similar to those of glasses, indicating that the aluminate liquids consist of AlOn polyhedral units on the vibrational time scale, rather than simple ionic species.

Effect of ionic strength on the kinetics of ionic and micellar reactions in aqueous solution

The effect of electrostatic forces on the rate of reaction between ions in aqueous solutions of intermediate ionic strength is studied in this paper. We consider the kinetics of reactions involving simple ionic species (1–1 and 2–2 electrolyte systems) as well as kinetic processes mediated by the presence of micellar ions (or other charged organizates). In the regime of ionic strength considered, dielectric saturation of the solvent in the vicinity of the reacting ions must be taken into account and this is done by introducing several models to describe the recovery of the solvent from saturation to its continuum dielectric behavior. To explore the effects of ion size, charge number, and ionic strength on the overall rate constant for the process considered, we couple the traditional theory of ionic reactions in aqueous solution with calculations of the electrostatic potential obtained via solution of the nonlinear Poisson–Boltzmann equation. The great flexibility of the nonlinear Poisson–Boltzmann theory allows us to explore quantitatively the influence of each of these effects, and our simulations show that the short-range properties of the electrostatic potential affect primarily kinetically controlled processes (to varying degrees, depending on the ionic system considered) whereas the down-range properties of the potential play a (somewhat) greater role in influencing diffusion-controlled processes. A detailed examination is made of ionic strength effects over a broad range of ionic concentrations. In the regime of low ionic strength, the limiting slope and intercept of the curve describing the dependence of log kD on I1/2/(1+I1/2) may differ considerably from the usual Debye–Hückel limiting relations, depending on the particular model chosen to describe local saturation effects. The results in the regime of high ionic strength for all models considered converge to the Smoluchowski limit, and thus differ significantly from the traditional Debye–Hückel results. As a specific application of our theory, we consider the reaction between pyrene solubilized in cetyltrimethylammonium bromide (CTAB) and e−aq. We estimate the chemical rate kR and then calculate the dependence of the overall rate on the ionic strength; the results obtained are found to be in excellent agreement with experiment.