Ion pair production

Figure 3 shows another example where colliding-beam experiments have produced results in excellent agreement with each other. This particular reaction is the recombination of ions with electrons producing ion-pair products, i.e. ... 

The concentration of small ions in the atmosphere is determined by 1) the rate of ion-pair production by the cosmic rays and radioactive decay due to natural radioactive substances, 2) recombination with negative ions, 3) attachment to condensation nuclei, 4) precipitation scavenging, and 5) transport processes including convection, advection, eddy diffusion, sedimentation, and ion migration under the influence of electric fields. A detailed differential equation for the concentration of short-lived Rn-222 daughter ions including these terms as well as those pertaining to the rate of formation of the... 

Radon daughter ions and the ionization caused by the decay chains of radon and thoron in indoor air play important roles both from the contribution made by the daughter product positive ions to internal dose and from the effects of ion-pair production on the indoor atmospheric electrical parameters. 

The ion pair production is independent of the radiation, causing the initial ionization. 

Negative-ion spectra were also recorded, and showed ions C5HxM(CO) (M = Co, = 1, 2 M = Mn, n = 0-3 M = V, n = 2, 3) but no ions M(CO) " were observed. The errors in measurements ( 3 m/e units) precluded an accurate determination of the value of x. These ions were probably formed by an ion-pair production process... 

Winters and Kiser also recorded the negative ion mass spectrum and observed the ions C5Hj,Co(CO)2 and CjHyCoCO- (jy = 3-5) which are formed by either electron capture or ion-pair production processes. 

The observation of C5FIj,Co(CO)2 at high ionizing energies (70 eV) indicates that the formation processes must involve ion-pair production, such as the two possible modes illustrated below. 

Ion pair production is observed with a wide range of electron energies above 15 eV. It is principally this process that leads to negative ion production under conventional El conditions. Ion pair production forms structurally insignificant very low-mass ions with a sensitivity that is 3—4 orders of magnitude lower than that for positive ion production. 

In ion-pair production the incident electron excites the molecule to an electronic level which leads to A+ and B (Figure 2.2c). 

The matrix isolation technique has been applied, in conjunction with the salt/molecule reaction technique, to model the high temperature gas phase reactions of alkali halide salt molecules. The reactions with Lewis acids such as SiFi, HF and CO2 yielded ion pair products which were quenched into inert matrices for spectroscopic study. Difficulties arising from lattice energy considerations in alkali halide salt reactions are minimized by the initial vaporization of the salt reactant. The reaction of such salt molecules with Lewis bases, including H2O and NH3, yielded complexes similar in nature to transition metal coordination complexes, with binding through the alkali metal cation to the base lone pair. 

Ionizing radiation arises from the photoelectric effect, the Compton effect, or ion pair production. Gamma radiation causes local and intense damage and may break chemical bonds. The primary target is the deoxyribonucleic acid (DNA) of the micro-organism. In addition, free radicals may be formed, such as peroxides that result in intracellular and extracellular peroxides by a chain reaction that causes damage. 

In Fig. 5, the relationship between the Townsend ionization coefficients (ion pair production) for air at atmospheric pressure at different temperatures and field strengths is given. 

Fig. 5 Effect of electric field strength and temperature on ion pair production.

The last contribution quoted in this section is a phosphine-free hydroformylation process based on a liquid triphasic system consisting of isooctane, water and trioctylmethylammonium chloride (TOMAC). The hydroformylation of model olefins required neat RhCls only as catalyst precursor. In the triphasic system, the catalyst is confined in the TOMAC phase, likely in the form of an ion pair. Products are obtained in excellent yields (> 90% at 80 °C) and high regioselectivity (>98%) in favour of the branched aldehyde in the case of styrene, while the exo isomer was obtained in >90% selectivity in the case of norbornene. The products were easily removed and the catalyst was recycled several times, with no leaching of rhodium into the organic phase. 

The adsorption system is in many respects similar to biological systems. Especially the smallness of the solvent reorientation energy, with Ag < and -AGg = A, of a donor-acceptor system with ion-paired product state in a diffusionless, semi-rigid environment, opens many possibilities to study certain aspects of electron transfer which are of importance to biological systems. 

Support for an electron transfer type of mechanism is gained from the observation that 4-/V-methyl pyridine thione (incapable of H-atom transfer) yields the ion pair product [Cr(CO)3(4-S-C5H4N-Me)(C5Me5)] + [Cr(CO)3Cp ]. 85 Mechanistic distinction between H-atom transfer and e /H+ transfer is challenging. Other mechanism may be possible as well. The important conclusion is that 4-pyridine thione that contains the good radical receptor S=C86 is much more reactive than the corresponding thiols in spite of the fact that the thione tautomer is more thermodynamically stable than its thiol counterpart. 

Heaps (1978a) derived a convenient parameterization of the rate of ion pair production by cosmic rays Qcr (cm-3s-1) as a function of... 

Figure 7.7. Rate of ionization provided by cosmic rays at different geomagnetic latitudes (0, 50, and 70°) and for minimum and maximum levels of solar activity. These values are compared to the ion pair production producted by direct and diffuse Lyman a. From Rosenberg and Lanzerotti (1979).

Figure 7.10. Rate of ion pair production by magnetospheric electrons (REP) in the subauroral zone. These values correspond to an annual average, and are compared to the effect of cosmic rays and the total ion pair production associated with the solar proton event (SPE) of August 1972. From Thorne...

The ionization rates of the major species, molecular nitrogen and oxygen, can be determined from the rate of total ion pair production, Q, if it is assumed that the fraction of ionization is proportional to the mass of the target particle (Rusch et al, 1981) ... 

Heaps, M.G., Parameterization of the cosmic ray ion-pair production rate above 18 km. Planet Space Sci 26, 513, 1978a. 

In the proportional counter region between Vj and F4, the number of electrons increases rapidly with applied voltage. This increase is the result of secondary ion-pair production caused by collisions between the accelerated electrons and gas molecules amplification... 

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