Ion vibration potential

Ion Vibration Potentials + Partial Molar Volumes Passynski Compressibility Ulich Entropy Ulich Mobility Zana and Yeager Averages Nearest Integer... 

FIGURE 26.1 Ion vibration potential or periodic excesses of either cations or anions caused by the relative motion of cations and anions. 

A look at Table IV will show the general simplicity of the spectra. This is due to the fact that ionization occurs by electron tunneling, which does not excite the ions vibrationally, as is the case with impact ionization. Thus the combination of field ionization and mass spectrometry has considerable analytical potentialities, when it is considered that acetone, for example, gives rise to 19 peaks of comparable intensity by impact ionization and shows no peaks over 0.1% except the parent in field ionization. 

Interface between two liquid solvents — Two liquid solvents can be miscible (e.g., water and ethanol) partially miscible (e.g., water and propylene carbonate), or immiscible (e.g., water and nitrobenzene). Mutual miscibility of the two solvents is connected with the energy of interaction between the solvent molecules, which also determines the width of the phase boundary where the composition varies (Figure) [i]. Molecular dynamic simulation [ii], neutron reflection [iii], vibrational sum frequency spectroscopy [iv], and synchrotron X-ray reflectivity [v] studies have demonstrated that the width of the boundary between two immiscible solvents comprises a contribution from thermally excited capillary waves and intrinsic interfacial structure. Computer calculations and experimental data support the view that the interface between two solvents of very low miscibility is molecularly sharp but with rough protrusions of one solvent into the other (capillary waves), while increasing solvent miscibility leads to the formation of a mixed solvent layer (Figure). In the presence of an electrolyte in both solvent phases, an electrical potential difference can be established at the interface. In the case of two electrolytes with different but constant composition and dissolved in the same solvent, a liquid junction potential is temporarily formed. Equilibrium partition of ions at the - interface between two immiscible electrolyte solutions gives rise to the ion transfer potential, or to the distribution potential, which can be described by the equivalent two-phase Nernst relationship. See also - ion transfer at liquid-liquid interfaces. 

In the next section it will be shown how these total solvation numbers for salts can be turned into individual solvation numbers for the ions in the salt by the use of information on what are called ionic vibration potentials, an electrical potential... 

Ionic Vibration Potentials Their Use in Obtaining the Difference of the Solvation Numbers of Two Ions in a Salt... 

In 1933 Peter Debye formulated a sophisticated theory about all this. He assumed, as is also intuitively obvious, that the supersonic emf, that is, the ionic vibration potential produced by the ultrasonic beam, would be proportional to the difference of the masses of the moving ions. Debye s expression can be reduced to... 

Obtaining the individual properties of ions with solvation numbers from measurements of ionic vibration potentials and partial molar volumes is not necessary in the study of gas phase solvation (Section 2.13), where the individual heats of certain hydrated entities can be obtained from mass spectroscopy measurements. One injects a spray of the solution under study into a mass spectrometer and investigates the time of flight, thus leading to a determination of the total mass of individual ions and adherent water molecules. 

Apart from neutron diffraction, what other method distinguishes between the static or equilibrium coordination number and the dynamic solvation number, the number of solvent molecules that travel with an ion when it moves One method is to obtain the sum of the solvation numbers for both cation and anion by using a compressibility approach, assuming that the compressibility of the primary solvation shell is small or negligible, then using the vibration potential approach of Debye to obtain the difference in mass of the two solvated ions. From these two measurements it is possible to get the individual ionic solvation numbers with some degree of reliability. 

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