Total single ionization cross section

III. Semiempirical Calculation of Total Single Ionization Cross Sections. 156... 

The experimentally determined HMDSO total single ionization cross section is compared with the result of a calculation using the modified additivity mle discussed before. The level of agreement between the experimentally determined and the calculated cross sections is better than 16% at all energies, which constitutes satisfactory agreement for such a complex target molecule. 

Figure 13 Singly differential cross sections for ionization of several molecular targets by 1-MeV protons are plotted as a function of the ejected electron energy. The cross sections are scaled by the effective number of target electrons in each molecule the effective number of electrons is defined as the total number of molecular electrons minus those of the K-shell. (From Refs. 49, 56, and 58.)...

It is notable that the photoionization cross sections does not appear in the BEB expression, although it is required in the Bethe model instead, a simple functional form has been assiuned (Kim and Rudd, 1994). A more elaborate model that does incorporate the photoionization cross section, referred to as the binary-encounter-dipole (BED) model, was also proposed by Kim and Rudd (1994). The BED model is suitable for calculation not only of the total ionization cross section but of the singly differential cross section, i.e., the eross section for a... 

Fig. 7. Absolute total single SiH4 ionization cross section as a function of electron energy. The various symbols refer to the following data triangles (A), Basner et a/., (1997a) circles ( ), Chatham et al. (1984) squares ( ), Krishnakumar and Srivastava (1995) diamonds (A), Haaland (1990) the dashed line represents a calculation using the modified additivity rule (see text for details), and the dotted line refers to the BEB calculation of Kim and coworkers (Ali et al., 1997).

The total and selected partial electron impact ionization cross sections of TMS are shown in Fig. 10. Also shown in Fig. 10 are the calculated total single TMS ionization cross sections from the modified additivity rule and from the BEB model of Kim and coworkers (Ali et al., 1997). There is reasonably good agreement between the two calculated cross sections and between the calculated cross sections and the measured cross section of Basner et al. (1996) (at least for impact energies below about 80 eV). The cross section of McGinnis etal. (1995) is considerably smaller than the two calculated cross sections and the measured cross section of Basner et al. (1996). 

Partial ionization cross sections for the formation of the ion dXm/z = 147, for the ion and the total single HMDSO ionization cross section are presented in Fig. 12. The cross section for the dominant ion (m/z = 147) reaches a... 

Total and counting ionization cross sections of a specific target system are the weighted and the simple sum of the various single and multiple partial cross sections, respectively ... 

It should be noted, however, that gaining a deeper insight into the problem of ionization phenomena is not the only reason for steady interest in the problem. Data on charged particle impact ionization is used both for industrial applications and for fundamental scientific research. For applications it is the collisions rates and total cross sections which are usually the most relevant. But in studies focused on the understanding of collision mechanisms of ionization processes, most of the information is lost in the total cross sections due to the integration over the momenta of the ejected electrons in the exit channel. Therefore it is the singly and doubly differential cross sections which are of... 

Figure 14. Double differential cross sections (ddcs — 2n dv v J for electron emission due to single, double, or triple ionization of Ar by 3.6-MeV/amu Au53+ ions. The DDCS for the specified recoil-ion charge states are added according to their relative contribution to the total cross section. CDW-EIS results (solid lines [73]) are shown along with the experimental data from Moshammer et at. [53], The experimental data are divided by 1.4. Cross sections at different ve are multiplied by factors of 10, respectively.

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