Electron impact molecular ionization

Khare, S. P.; Tomar, Surekha; Sharma, M. K.

doi:10.1088/0953-4075/33/2/101

Cited by 3 publications

(2 citation statements)

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“…For the CH 4 molecule the TICS difference between both methods is less than 3%. 28 In this paper TICS for CF 4 , CHF 3 , CH 2 F 2 , and CHF 3 molecules have been computed by the Khare-BEB method and Fig. 2 shows, as an illustration, the CF 4 ICS profiles.…”

Section: A the Kim-beb And Khare-beb Methodsmentioning

confidence: 99%

Evaluation of the computational methods for electron-impact total ionization cross sections: Fluoromethanes as benchmarks

Torres

Martı́nez

Rayo

et al. 2001

The Journal of Chemical Physics

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The experimental electron-impact total ionization cross sections ͑TICSs, ICSs͒ of CF 4 , CHF 3 , CH 2 F 2 , and CH 3 F fluoromethanes reported so far and a new set of data obtained with a linear double focusing time-of-flight mass spectrometer have been compared with the ab initio and ͑semi͒empirical based ICS available methods. TICSs computational methods include: two approximations of the binary-encounter dipole ͑BED͒ referred to hereafter as Kim ͑Kim-BEB͒ and Khare ͑Khare-BEB͒ methods, the Deutsch and Märk ͑DM͒ formalism, also requiring atomic and molecular ab initio information, the modified additivity rule ͑MAR͒, and the Harland and Vallance ͑HV͒ methods, both based on semiempirical or empirical correlations. The molecular ab initio information required by the Kim, Khare, and DM methods has been computed at a variety of quantum chemistry levels, with and without electron correlation and a comprehensive series of basis sets. The general conclusions are summarized as follows: the Kim method yields TICS in excellent agreement with the experimental method; the Khare method provides TICS very close to that of Kim at low electron-impact energies ͑Ͻ100 eV͒, but their Mott and Bethe contributions are noticeably different; in the Kim and Khare approximations the electron correlation methods improve the fittings to the experimental profiles in contrast with the large basis sets, that leads to poorer results; the DM formalism yields TICS profiles with shapes similar to the experimental and the BEB methods, but consistently lower and with the profiles maxima shifted towards lower incident electron energies; the MAR method supplies very good ICS profiles, between those of BEB and DM methods; finally, the empirical HV method provides rather poor fittings concomitant with the simplicity and the few empirical parameters used.

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Section: A the Kim-beb And Khare-beb Methodsmentioning

confidence: 99%

Evaluation of the computational methods for electron-impact total ionization cross sections: Fluoromethanes as benchmarks

Torres

Martı́nez

Rayo

et al. 2001

The Journal of Chemical Physics

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“…For many cases the deviation from experiment is within 5-15 % at the peak, with the BED model performing somewhat better than the BEB model ͓6-10͔. More recently, Khare et al ͓11,12͔ introduced their version of the binaryencounter-dipole model. Again the Bethe cross section was used to describe long-range dipole collisions.…”

Section: Introductionmentioning

confidence: 99%

Convergent series representation for the generalized oscillator strength of electron-impact ionization and an improved binary-encounter-dipole model

Huo

2001

Phys. Rev. A

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The use of the Bethe cross section in the binary-encounter-dipole ͑BED͒ model for electron-impact ionization is studied. While the dipole contribution in the Born approximation accounts for the longest-range interaction in electron-neutral atom/molecule inelastic collisions at any incident energy, the Bethe formula is applicable only at high energies. To derive a suitable representation of the Born cross section for dipoleallowed transitions, a convergent series representation for the generalized oscillator strength ͑GOS͒ of electronimpact ionization is studied. It is shown that by transforming to a new variable determined by the location of the singularities of the GOS on the complex plane of momentum transfer K, a series representation for the GOS is obtained that is convergent at all physically attainable values of K. An approximate representation of the GOS that truncates the series representation to the first three terms is also given. The approximate GOS describes the interaction of the electron with a shielded dipole potential and satisfies both Lassettre's limit theorem at Kϭ0 and the asymptotic behavior at large K derived by Rau and Fano ͓A. R. P. Rau and U. Fano, Phys. Rev. 162, 68 ͑1967͔͒. The dipole-Born cross section so obtained is applicable at all incident energies and goes to the Bethe cross section at the high-energy limit. It provides a more suitable representation of the dipole contribution in the BED model than the Bethe cross section and is valid over the entire energy range. A similar analysis of the optical-oscillator strength ͑OOS͒ as a function of the complex momentum for the ejected electron k p , plus the requirement that the OOS satisfies both the low-and high-k p limits produces an analogous series representation for the OOS. An approximate one-term representation of the OOS is also developed that can be used in modeling calculations. Numerical examples of total ionization cross sections of N 2 , H 2 O, CO 2 , CH 4 , and CF 4 using the new analytical representation are presented to illustrate the applicability of the improved BED model.

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Plasma Chemical Reactions (P Models)

2002

Physical and Chemical Processes in Gas Dynamics

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Electron impact molecular ionization

Abstract: Khare et al observed that in the binary-encounter Bethe approximation their ionization cross sections were very close to those obtained by the method of Kim and Rudd. An explanation has been advanced for the above observation.

Cited by 3 publications

References 3 publications

Evaluation of the computational methods for electron-impact total ionization cross sections: Fluoromethanes as benchmarks

Evaluation of the computational methods for electron-impact total ionization cross sections: Fluoromethanes as benchmarks

Convergent series representation for the generalized oscillator strength of electron-impact ionization and an improved binary-encounter-dipole model

Plasma Chemical Reactions (P Models)

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