Electron capture ionization process

The energies involved in the ionization ) or electron capture (EA) process are... 

Mathematical models of the electron-capture process are based on the stirred reactor model of Lovelock [145] and the kinetic model of Wentworth [117,142,146] as further modified by others [129,134-136,147-150]. The ionization ch2uaber is considered... 

Charge exchange is important all along the high-LET tracks. The effective ionic charge is determined by cross sections of electron capture and loss, which depend predominantly on the ionic velocity. Electron loss may be simply described by an ionization of the incident ion in its own reference frame due to the impact of medium electrons and nuclei. Following Bohr (1948), Mozumder et al. (1968) wrote the cross section for this process as1... 

In Eq. (3.4), the contributions of both the nuclei and the electrons are considered. The maximum energy transfer for electrons is (l/4)mv2, but since their contribution to the loss cross section is small, no great error is committed in taking the maximum energy transfer as 2mv2 for all ionizations represented in Eq. (3.4). Electron capture is a three-body process best visualized as ionization of a molecule of the medium with the ejected electron having a speed v at least equal to that of the incident ion, followed by capture of that electron in an orbit around the impinging ion. Mozumder et al. (1968) modified an earlier formula of Bohr (1948) and wrote the capture cross section as... 

Normally, in impact ionization, outer electrons are removed. Infrequently, however, an inner electron may be ejected or a K-process may occur such as an orbital electron capture or /3-decay. In such cases, the result is an electronic rearrangement, in preference to emission. Since enough energy is available, frequently the resultant ion is multiply charged. The cross section for this process follows the usual Bethe-type variation -T 1 ln(BT), where B is a constant (Fiquet-Fayard et al., 1968). In charged particle irradiation, the amount of energy lost in the K-processes is very small, usually much less than 1%. On the other hand, some specific effect may be attributable to that that is, experiments can be so designed. 

A little recognized systematic error in the calculation of accurate masses of, for example, small radical cation molecular ions (as in electron ionization (El)) or protonated molecular ions (as seen in the soft ionization methods) is the fact that the electron has a small, but finite mass. The accurate masses of radical cations, in which a valence electron has been removed, of anions that have been created by capture of an electron, and of protonated species produced by soft ionization processes, should take into consideration this small mass difference [19]. For example, there is a small difference between the relative atomic mass of a neutral hydrogen atom and a proton. The accepted accurate mass of 1H° is 1.007825 Da. The accurate mass of 1H+ is 1.007276 Da. To be completely correct, expected accurate masses of protonated molecular ions, [M+H]+, produced by electrospray should be calculated using the mass of one H+, rather than all of neutral hydrogen atoms. Mamer and Lesimple do acknowledge, however, that, for large molecules, the error is of little consequence. 

For an ion, the cross section for electron capture (EC) roughly increases with the square of the ionic charge. [137] This makes multiply charged ions as produced by electrospray ionization (ESI, Chap. 11) the ideal targets for this process, e.g. ... 

The electron capture detector is the result of a series of developments which were initiated in 1951 by D. J. Pompeo and J. W. Otvos (14) of the Shell Company s development laboratory in California. The device they invented was a beta-ray ionization cross-section detector (Section 5.8). Deal et al. (15) at the Shell laboratory in California and Boer (16) in Amsterdam modified the detector, used originally to monitor effluents of a large scale plant process, for applications in GC. From the limited success of the detector. Lovelock (17) produced the beta-ray argon detector in 1958 (Section 5.8). This modification substituted argon as the carrier gas and placed a potential of 1000 V across the electrodes. Argon passing between the electrodes absorbed radiation and formed a metastable species with energy (11.6 eV) sufficient to ionize most substances. Proposed mechanisms for this process are ... 

The first reported study of the behaviour of double differential cross sections for positron impact ionization was that of Moxom et al. (1992) these workers conducted a search for electron capture to the continuum (ECC) in positron-argon collisions. In this experiment electrons ejected over a restricted angular range around 0° were energy-analysed to search for evidence of a cusp similar to that found in heavy-particle collisions (e.g. Rodbro and Andersen, 1979 Briggs, 1989, and references therein), which would be the signature of the ECC process. 

The formation of C5H5Co was observed at low ionizing energy, and is probably formed by a dissociative electron capture process. 

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