Elementary ions

Assigning a mechanism for the formation of products resulting from ionic intermediates is aided by our knowledge of the probable primary ions and the elementary ion-molecule reactions which they may undergo. The second subject to be examined is the applicability of fragmentation patterns and mass spectrometric ion-molecule reaction studies to radiolysis conditions. Lastly, the formation and the chemistry of the ionic species in ethylene radiolysis will be summarized. 

Using a simple electrostatic interaction-based model factored into reaction rate theory, the energy barrier for ion hopping was related to the cation hydration radius. The conductance versus water content behavior was suggested to involve (1) a change in the rate constant for the elementary ion transfer event and (2) a change in the membrane microstructure that affects conduction pathways. 

According to F. Kohlrausch,28 these anomalous results are not due to the friction between the elementary ions and the water mols., but rather to the friction between the water mols. and complexes—hydrated ions. The absolute velocity of transport of the ions is calculated by dividing the transport numbers by 96540, the electric charge carried by the transported ions. Lithium salts are also strongly ionized in many non-aqueous solns.—e.g. methyl or ethyl alcohol. P. Lenard and co-workers calculate the number, n, of molecules of water combined with the ions in aq. soln., and, r, the radius of the ions ... 

The polarizability of a certain donor is determined by the electronegativity of its coordinating donor atom, in conjunction with the properties of neighbouring atoms within the ligand. If the donor atom exists as an elementary ion, its own electronegativity is therefore the only factor of importance. A decrease of this quantity will imply an increase of the polarizability and, consequently, a stronger tendency to form... 

Figure 42 shows the basic elementary ion migration processes in a low defective isotropic ion conductor with a mobility in the A-sublattice. The vacancy mechanism (Fig. 42 top) can be described by a transport process (Zv= effective charge of the A-vacancy) such as... 

Spectroscopic determination of atomic species can only be performed on a gaseous medium in which the individual atoms or elementary ions, such as Fe, Mg, or Al, are well separated from one another. Consequently, the first step in all atomic spectroscopic procedures is atomization, a process in which a sample is volatilized and decomposed in such a way as to produce gas-phase atoms and ions. The efficiency and reproducibility of the atomization step can have a large influence on the sensitivity, precision, and accuracy of the method. In short, atomization is a critical step in atomic spectroscopy. 

Atomization is a process in which a sample is converted into gas-phase atoms or elementary ions. 

Once the sample has been converted into gaseous atoms or elementary ions, various types of spectroscopy can be performed. We consider here optical and mass spectrometric methods. 

In all atomic spectroscopic techniques, we must atomize the sample, converting it into gas-phase atoms and ions. Samples are most commonly presented to the atomizer in solution form, although we sometimes introduce gases and solids. Hence, the atomization device must perform the complex task of converting analyte species in solution into gas-phase free atoms or elementary ions, or both. 

When a nebulized sample is carried into a flame, desolvation of the droplets occurs in the primary combustion zone, which is located just above the tip of the burner, as shown in Figure 28-12. The resulting finely divided solid particles are carried to a region in the center of the flame called the inner cone. Here, in this hottest part of the flame, the particles are vaporized and converted to gaseous atoms, elementary ions, and molecular species (see Figure 28-6). Excitation of atomic emission spectia also takes place in this region. Finally, the atoms, molecules, and ions... 

Chemical interferences are usually specific to particular analytes. They occur in the conversion of the solid or molten particle after desolvation into free atoms or elementary ions. Constituents that influence the volatilization of analyte particles cause this type of interference and are often called solute volatilization interferences. For example, in some flames the presence of phosphate in the sample can alter the atomic concentration of calcium in the flame owing to the formation of relatively nonvolatile complexes. Such effects can sometimes be eliminated or moderated by the use of higher temperatures. Alternatively, releasing agents, which are species that react preferentially with the interferent and prevent its interaction with the analyte, can be used. For example, the addition of excess Sr or La minimizes the phosphate interference on calcium because these cations form stronger phosphate compounds than Ca and release the analyte. 

These relationships show the importance of d. When the elementary ions are large (weak salts) the size (pc) and capacity (nc) of the clusters become large. The radius pc can be expressed as a function of a limiting concentration c0 at the surface of the cluster ... 

Collisions with atomic clusters represent a relatively new branch of collision physics as compared to the well established fields of ion-atom collisions [1] and ion-solid interaction [2]. The study of cluster collisions is of particular interest and importance because it offers the possibility, to tackle bridge-building questions (like the transition from individual excitations in the elementary ion-atom collision to the macroscopic stopping power in solids) as well as fundamental problems (like phase transitions in finite systems). 

This chapter deals with optical atomic, emission spectrometry (AES). Generally, the atomizers listed in Table 8-1 not only convert the component of samples to atoms or elementary ions but, in the process, excite a fraction of these species to higher electronic stales.. 4, the excited species rapidly relax back to lower states, ultraviolet and visible line spectra arise that are useful for qualitative ant quantitative elemental analysis. Plasma sources have become, the most important and most widely used sources for AES. These devices, including the popular inductively coupled plasma source, are discussedfirst in this chapter. Then, emission spectroscopy based on electric arc and electric spark atomization and excitation is described. Historically, arc and spark sources were quite important in emission spectrometry, and they still have important applications for the determination of some metallic elements. Finally several miscellaneous atomic emission source.s, including jlanies, glow discharges, and lasers are presented. 

For a given water content and by applying the Stokes-Einstein equation and the rate process to ionic migration s , it is possible to calculate, for two dilferent ions, the difference between their activation free energies for the elementary ion transfer reactions, the proton being chosen as the reference ion... 

Reactions (2) and (3) occurring in methane were also observed by Stevenson and co-workers in 1955 in the ion source of a laboratory mass spectrometer and launched an important era that connected elementary ion-molecule... 

Fig. 10 Standard Gibbs energy profile for an elementary ion-transfer reaction.

The simplest elementary ions, considering the case of the H2—O2 fuel cell (similar logic may be applied to other eCMRs), are H+ and However, other more complex ions are often formed from these elementary ions and a vehicle molecule (Q) that ferries the elementary ion across the electrolyte and then returns for the next payload, e.g., water molecule, i.e., (Q) = (H2O), which forms H30 ion at the anode as the ion-carrier species, i.e., H+ + (H2O) <= H30+. As another example, an oxygen anion may form the hydroxyl ion with water ((Q) = (H2O)) in the cathode of an AFC, i.e., + (H20) 20H . On the other hand, in an molten-carbonate fuel cell... 

One of the paths of an elementary ion-molecule process occurs via a long-lived complex. The existence of such complexes was first found for reaction -1- HgO -> + OH in measuring the initial kinetic energy of HsO ... 

Frankevich, E. L. Mass Spectrometric Study of Elementary Ion-Molecule Processes in the Gas Phase. Thesis. (In Russ.) Moscow, Inst, of Chem. Phys., Acad. Sci. USSR, 1957, p. 148. 

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