Total ionization

If we compare the calculated total ionization potential, IP = 4.00 hartiees, with the experimental value, IP = 2.904 hartiees, the result is quite poor. The magnitude of the disaster is even more obvious if we subtract the known second ionization potential, IP2 = 2.00, from the total IP to find t c first ionization potential, IPi. The calculated value of IP2, the second step in reaction (8-21) is IP2 = Z /2 = 2.00, which is an exact result because the second ionization is a one-election problem. For the first step in reaction (8-21), IPi (calculated) = 2.00 and IPi(experimental) = 2.904 — 2.000 =. 904 hartiees, so the calculation is more than 100% in error. Clearly, we cannot ignore interelectronic repulsion. 

The mass spectra of phenylthiazoles are characterized by the presence of intense molecular ion peaks, due to the aromatic nature of the molecules, which represent 35, 41, and 44% of the total ionization for 2-, 4-, and 5-phenylthiazoles, respectively. 

Plot of Total Ionization (Ordinate) vs Mass Spectrum Index Number. . . Typical Laced Concrete Wall. 

Fig 12a Plot of total ionization (ordinate) vs mass spectrum... 

The main primary fragment ions of diaryl sulfoxides 13 and 14 have the structures 16a or 16b(C8H7S02 + m/z 167) and the ion m/z 152 (17) can be obtained from both by the loss of CH3 (equation 5)13. Ions 16a and 16b are formed from the sulfenate ester structure of the molecular ions of 13 and 14 through a cyclization process and a simultaneous loss of the other O Ar part. A similar ortho effect is not possible in 15 and hence its most intense ion is M+ (23% of the total ionization in comparison with 2.7 and 0.6% for 13 and 14, respectively) and its primary fragments are typical for a normal diaryl sulfoxide. 

General. The use of alpha particles instead of electrons as in conventional ion-molecule reaction mass spectrometers introduces a difference in primary ionization conditions which is not as great as might be supposed. Thus, the primary ion mass spectra produced by alpha particles are very similar to these produced by say 70-e.v. electrons (30). Secondary electrons produced by the alpha particles are responsible for more than 50% of the total ionization. The energies of these electrons peak in the range 20-100 e.v. so that again the primary ions will be similar to those produced by 70-e.v. electrons. 

Total Ionization with Movable Collimating Slit. To locate the region from which the sample originates, some experiments were done with a movable collimating slit. The slit was 1x5 mm. and was... 

C2H5(NO)2+ was also observed. The total ionization was essentially unaffected by adding NO, and no NO + could be detected. 

Application to Ethylene Radiolysis. The predominant ions in the mass spectrum of ethylene (1) are ethylene, vinyl, and acetylene ions, which together account for over 85% of the total ionization. A total of 38% of all ions are C2H4+, and since kF(ethylene) = 25.9 e.v./ion pair, the parent ion should be produced with a yield of at least 1.5 ions/100 e.v. absorbed in ethylene. Similar calculations for the probable yields of the other major ions lead to estimates of 0.96 vinyl ions/100 e.v. and 0.94 acetylene ions/100 e.v. Successive dissociations are relatively unimportant in ethylene. 

Of course, it is possible to contemplate experiments that examine photoionization of oriented chiral molecules. An expression has been given for the angle integrated (total) ionization cross-section in such circumstances [48] and CDAD-type measurements have been reported on adsorbed chiral molecules [49, 50], but the interplay of natural and geometric chirality in angle-resolved dichroism measurements remains very much a topic for future investigation. 

Primary Ionization—(1) In collision theory the ionization produced by the primary particles as contrasted to the "total ionization" which includes the "secondary ionization" produced by delta rays. (2) In counter tubes the total ionization produced by incident radiation without gas amplification. 

Total Ionization—The total electric charge of one sign on the ions produced by radiation in the process of losing its kinetic energy. For a given gas, the total ionization is closely proportional to the initial ionization and is nearly independent of the nature of the ionizing radiation. It is frequently used as a measure of absorption of radiation energy. 

Quantum mechanical and selected semiclassical and semiempirical methods for the calculation of electron impact ionization cross sections are described and their successes and limitations noted. Experimental methods for the measurement of absolute and relative ionization cross sections are also described in some detail. Four theoretical methods, one quantum mechanical and three semiclassical, have been used to calculate cross sections for the total ionization of the inert gases and small molecules and the results compared with experimental measurements reported in the literature. Two of the theoretical methods, one quantum mechanical and one semiclassical, have been applied to the calculation of orientation-dependent electron impact ionization cross sections and the results compared with recent experiments. 

Partial wave methods have been widely used and tested on a variety of systems (see reference 19 and references therein). They are usually accurate to better than 50% for total ionization cross sections of light atoms. Very heavy atoms have been less successfully treated due to the increasing contributions of resonances and... 

Figure 2. Total ionization source of Rapp et al59 where F is the filament electron lenses are labeled 1, 2 and 3 guard plates G ion collector C1 and field plate C2 electron collector shield S electron collector cylinder T and electron collector plate P.

Figure 3. Total ionization source of Tate and Lozier70 where F is the filament L the electron lens K a cylindrical gauze defining an equipotential electron path G discs E ion collection cylinder D electrometer guard cylinder C shield T electron collection cylinder and P electron collector.

Table 1. Measured and Calculated Maximum Total Ionization Cross Sections in A2...

Table 2. Relationships for the Calculation of Maximum Total Ionization Cross Sections Based on Literature Experimental Data...

Using the ab initio EM method, the steric ratio is taken as the calculated cross section for electron approach along the molecular axis towards the positive end of the dipole divided by that for approach towards the negative end of the dipole. The model predicts a steric ratio of 1.41 for the total ionization of CH3C1 that is, both the sign and magnitude are in accord with the experimental measurements. The... 

Figure 12. Steric ratio for the total ionization ofCHsCI as a function of electron energy calculated using the DM theory.

The total ionization cross section is found from (4.18) ... 

Another procedure for calculating the W value has been developed by La Verne and Mozumder (1992) and applied to electron and proton irradiation of gaseous water. Considering a small section Ax of an electron track, the energy loss of the primary electron is S(E) Ax, where S(E) is the stopping power at electron energy E. The average number of primary ionizations produced over Ax is No. Ax where o. is the total ionization cross section and N is the number density of molecules. Thus, the W value for primary ionization is 0)p = S(E)/No.(E). If the differential ionization cross section for the production... 

Following Platzman (1967), Magee and Mozumder (1973) estimate the total ionization yield in water vapor as 3.48. The yield of superexcited states that do not autoionize in the gas phase is 0.92. Assuming that all of these did autoion-ize in the liquid, we would get 4.4 as the total ionization yield. This figure is within the experimental limits of eh yield at 100 ps, but it is less than the total experimental ionization yield by about 1. The assumption of lower ionization potential in the liquid does not remove this difficulty, as the total yield of excited states in the gas phase below the ionization limit is only 0.54. 

The first subnanosecond experiments on the eh yield were performed at Toronto (Hunt et al., 1973 Wolff et al., 1973). These were followed by the subnanosecond work of Jonah et al. (1976) and the subpicosecond works of Migus et al. (1987) and of Lu et al. (1989). Summarizing, we may note the following (1) the initial (-100 ps) yield of the hydrated electron is 4.6 0.2, which, together with the yield of 0.8 for dry neutralization, gives the total ionization yield in liquid water as 5.4 (2) there is -17% decay of the eh yield at 3 ns, of which about half occurs at 700 ps and (3) there is a relatively fast decay of the yield between 1 and 10 ns. Of these, items (1) and (3) are consistent with the Schwarz form of the diffusion model, but item (2) is not. In the time scale of 0.1-10 ns, the experimental yield is consistently greater than the calculated value. The subpicosecond experiments corroborated this finding and determined the evolution of the absorption spectrum of the trapped electron as well. 

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