Polarizabilities gases

It is a known fact that finely divided carbon can adsorb many gases, a property which is utilized in gas masks. Here the adsorption depends on the van der Waals-London forces, from which it follows that all strongly polarizable gases will be adsorbed, and, further, that a carbon mask is not suitable for the adsorption of CO. In practice, the efficacy of carbon for the adsorption of gases can be increased by adding other, usually ionic materials. 

The adsorption of carbon dioxide on DD3R amounts to 40.5 % of the adsorption on zeolite Na-A (7.62 wt% and 18.8 wt% respectively). It is dear that the preference of zeolite Na-A for adsorption of polarizable gases is larger than that of DD3R Charged frameworks as well as the presence of cations in the framework stmcture can induce dipoles within the adsorbate molecule, resulting in stronger interactions with the adsorbent. 

Most of the early published investigations on models of ion mobility were made by physicists in relatively simple systems, mainly those in which monoatomic ions drifted through an inert monoatomic or diatomic neutral gas. - - - This is evident in Table 1 given in Appendix 1 of Reference 4. As this chapter is concerned with polyatomic ions drifting through polar or polarizable gases, especially air, there are not many detailed experimental and theoretical studies that can be cited as relevant. ... 

Another factor that affects the ion radius and the ion mass arises from the observation that ions drifting in polarizable gases, especially at low temperatures, tend to form clusters with the drift gas molecules. Thus, the mass of the ion may be incremented from its original mass m by clustering with n neutral molecules, each having a mass of M, such that its effective mass m fis altered per Equation 10.24 ... 

While Onsager s formula has been widely used, there have also been numerous efforts to improve and generalize it. An obvious matter for concern is the cavity. The results are very sensitive to its size, since Eqs. (33) and (35) contain the radius raised to the third power. Within the spherical approximation, the radius can be obtained from the molar volume, as determined by some empirical means, for example from the density, the molar refraction, polarizability, gas viscosity, etc.90 However the volumes obtained by such methods can differ considerably. The shape of the cavity is also an important issue. Ideally, it should be that of the molecule, and the latter should completely fill the cavity. Even if the second condition is not satisfied, as by a point dipole, at least the shape of the cavity should be more realistic most molecules are not well represented by spheres. There was accordingly, already some time ago, considerable interest in progressing to more suitable cavities, such as spheroids91 92 and ellipsoids,93 using appropriate coordinate systems. Such shapes... 

The potential generated outside the sphere contains two contributions, i.e., one from the incident field (first term) and another from the field of an electric dipole located at the center of the sphere with polarizability ga oriented in the direction of the incident field (second term). Thus the local electric potential at position r, in the small-sphere approximation, is equivalent to that generated by the applied incident field and a reflected field produced by the metal sphere. 

The method for calculating effective polarizabilitie.s wa.s developed primarily to obtain values that reflect the stabilizing effect of polarizability on introduction of a charge into a molecule. That this goal was reached was proven by a variety of correlations of data on chemical reactivity in the gas phase with effective polarizability values. We have intentionally chosen reactions in the gas phase as these show the predominant effect of polarizability, uncorrupted by solvent effects. 

Fundamental enthalpies of gas-phase reactions such as proton affinities or gas-phase acidities can be correlated with the values of the Inductive and the polarizability effect. 

When monochromatic radiation falls on a molecular sample in the gas phase, and is not absorbed by it, the oscillating electric field E (see Equation 2.1) of the radiation induces in the molecule an electric dipole which is related to E by the polarizability... 

This is opposite from the order in solution as revealed by the pK data in water and DMSO shown in Table 4.14. These changes in relative acidity can again be traced to solvation effects. In the gas phase, any substituent effect can be analyzed directly in terms of its stabilizing or destabilizing effect on the anion. Replacement of hydrogen by alkyl substituents normally increases electron density at the site of substitution, but this effect cannot be the dominant one, because it would lead to an ordering of gas-phase acidity opposite to that observed. The dominant effect is believed to be polarizability. The methyl... 

Another progress in our understanding of the ideally polarizable electrode came from theoretical works showing that the metal side of the interface cannot be considered just as an ideal charged plane. A simple quantum-mechanical approach shows that the distribution of the electron gas depends both on the charge of the electrode and on the metal-solution coupling [12,13]. 

Suppose now, that the material is a gas comprising N atoms each of polarizability o in a volume V. When an electric field E is applied, each atom acquires an induced dipole moment aE and so the polarization is... 

The polarizability of the inert gas atoms does indeed increase with their size, as can be seen from Table 17.1. 

A problem with studies on inert gas is that the interactions are so weak. Alkali halides are important commercial compounds because of their role in extractive metallurgy. A deal of effort has gone into corresponding calculations on alkali halides such as LiCl, with a view to understanding the structure and properties of ionic melts. Experience suggests that calculations at the Hartree-Fock level of theory are adequate, provided that a reasonable basis set is chosen. Figure 17.7 shows the variation of the anisotropy and incremental mean pair polarizability as a function of distance. 

HC1 2H20 and HC1 3H20 it readily forms a hydroquinone clathrate. Ammonia, on the other hand, does not form clathrates with either water or hydroquinone. Molecules with a very low polarizability (He, Ne, H2) are not known to form clathrate solutions by themselves, but they do help to stabilize the clathrate of a more polarizable solute simultaneously present.47 It is almost needless to say that in the following we shall only consider those hydrates which are in fact clathrates and which are frequently referred to as gas hydrates/ although the molecules of certain volatile liquids may also be included. 

Figure 5.19. The physical origin of NEMCA When a metal counter electrode (C) is used in conjunction with a galvanostat (G) to supply or remove ions [O2 for the doped Zr02 (a), Na+ for P"-A1203 (b)] to or from the polarizable solid electrolyte/catalyst (or working electrode, W) interface, backspillover ions [O6 in (a), Na5+ in (b)] together with their compensating charge in the metal are produced or consumed at the tpb between the three phases solid electrolyte/catalyst/gas. This causes an increase (right) or decrease (left) in the work function of the gas-exposed catalyst surface. In all cases AO = eAUWR where AUWr is the overpotential measured between the catalyst and the reference electrode (R).

Ammonia is a pungent, toxic gas that condenses to a colorless liquid at — 33°C. The liquid resembles water in its physical properties, including its ability to act as a solvent for a wide range of substances. Because the dipole moment of the NH3 molecule (1.47 D) is lower than that of the H20 molecule (1.85 D), salts with strong ionic character, such as KCI, cannot dissolve in ammonia. Salts with polarizable anions tend to be more soluble in ammonia than are salts with greater ionic character. For example, iodides are more soluble than chlorides in ammonia. Liquid ammonia undergoes much less autoprotolysis than water ... 

Dispersive forces are more difficult to describe. Although electric in nature, they result from charge fluctuations rather than permanent electrical charges on the molecule. Examples of purely dispersive interactions are the molecular forces that exist between saturated aliphatic hydrocarbon molecules. Saturated aliphatic hydrocarbons are not ionic, have no permanent dipoles and are not polarizable. Yet molecular forces between hydrocarbons are strong and consequently, n-heptane is not a gas, but a liquid that boils at 100°C. This is a result of the collective effect of all the dispersive interactions that hold the molecules together as a liquid. 

Considerable effort has been expended on Ag atoms and small, silver clusters. Bates and Gruen (10) studied the spectra of sputtered silver atoms (a metal target was bombarded with a beam of 2-keV, argon ions produced with a sputter ion-gun) isolated in D, Ne, and N2. They found that an inverse relationship between Zett of the metal atom and the polarizability of rare-gas matrices (as determined from examination of... 

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