Cross section total ionization

In the previous section we have considered only processes which lead to electron loss to the continuum. Electron transfer is, in a sense, a more delicate process involving discrete states in both the initial and final configuration. Even so charge transfer cross sections can become very large in near resonant collisions and can completely dominate inner shell ionization total cross sections. ... 

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.

First, in cases where the transition (ionization) rate is small, the total cross section will be given by ... 

Figure 8 Total cross sections for ionization, excitation, and elastic scattering of electrons in water vapor in the energy range of 10 eV to 10 MeV.

Figure 11 Total cross sections due to proton (left) and alpha particle (right) impact on water vapor. Total ionization cross sections were obtained by fitting polynomial functions to the experimental data [198-200]. The curve for excitation was assumed to be the same between protons and alpha particles. Elastic scattering was evaluated by the classical mechanics trajectory calculations [Eqs. (16) and (17)].

Equally as interesting as the size of the total cross section is the distribution of the final states subsequent to mixing. Examining the adiabatic field ionization signals of Kachru et al., 30 it appears that only the lowest Stark states nearest to the... 

Fig. 11.28 Measured cross section for ionization of n = 46 (35 < n < 50) D atoms in collisions with N2 vs the kinetic energy Wu of the deuterium atom (O), measured cross section for destruction of n = 46 D atoms ( ) and n = 71 D atoms (A) in collisions with N2 (ref. 116). For comparison, Kennerly s measured total cross section for free electron-N2...

Carrying out the sum in formula (4.34) over all the possible states n, we get the total cross section of excitation from the ground state crex. Adding to it the ionization cross section cr(. we obtain the total cross section of inelastic scattering o-tot, which can be presented as... 

As the positron energy is raised above the positronium formation threshold, EPs, the total cross section undergoes a conspicuous increase. Subsequent experimentation (see Chapter 4) has confirmed that much of this increase can be attributed to positronium formation via the reaction (1.12). Significant contributions also arise from target excitation and, more importantly, ionization above the respective thresholds (see Chapter 5). In marked contrast to the structure in aT(e+) associated with the opening of inelastic channels, the electron total cross section has a much smoother energy dependence, which can be attributed to the dominance of the elastic scattering cross section for this projectile. 

Fig. 2.14. Compendium of total cross section data for positron-noble gas and electron-noble gas scattering. The arrows refer to thresholds for (in order of increasing energy) positronium formation (positrons only), excitation and ionization. (From Kauppila and Stein, 1982.)...

The first studies of positron impact ionization were based around the TOF systems originally developed for total cross section measurements see section 2.3 and, for example, Griffith et al. (1979b), Coleman et al. (1982), Mori and Sueoka (1984, 1994), though only the latter workers, as described in section 5.1, claimed to be able to distinguish between ionization and excitation using the TOF technique. 

Rapp, D. and Englander-Golden, P. (1965). Total cross sections for ionization and attachment in gases by electron impact I. Positive ionization. J. Chem. Phys. 43 1464-1479. 

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