Electron approximation cross section

Blaha, M. Davis, J. Electron Ionization Cross Sections in the Distorted Wave Approximation. N.R.L. Memorandum Report 4245, Naval Research Laboratory, Washington, DC, 1980. 

The electronic optical cross section a(hv) can be expressed in the dipole approximation as... 

Abstract. Cross sections for electron transfer in collisions of atomic hydrogen with fully stripped carbon ions are studied for impact energies from 0.1 to 500 keV/u. A semi-classical close-coupling approach is used within the impact parameter approximation. To solve the time-dependent Schrodinger equation the electronic wave function is expanded on a two-center atomic state basis set. The projectile states are modified by translational factors to take into account the relative motion of the two centers. For the processes C6++H(1.s) —> C5+ (nlm) + H+, we present shell-selective electron transfer cross sections, based on computations performed with an expansion spanning all states ofC5+( =l-6) shells and the H(ls) state. 

Before discussing possible mechanisms that could explain these results, it is worthwhile comparing the time constants to results from previous electron-induced surface chemical reactions. The extracted time constant, t, equals 1/ct/, where/is the X-ray flux density and % is the photolysis cross section. Using approximate values of the beam area (3 x 10 4 cm2) and X-ray flux (3.5 x 10n ph/s), yields a flux density of 1.7 x 1015 ph/s cm2 and a a of 6 x 10-19 cm2. Our results show that it is the secondary electrons that are inducing the chemical changes. Therefore, it is more applicable to use the secondary electron flux to compute the cross section. An upper bound to this is given by the TEY flux density. This is determined from the measured sample current of 3.8 nA or 2.4 x 1010 e/s, which results in a cross section of 9 x 10 18 cm2 (9 Mb) This value compares fairly well with reported dissociative electron impact cross sections for CO production from condensed films of acetone (9.6 Mb) [124] or methanol (4.2 Mb) [125] via a DEA mechanism. In the present case a DEA mechanism, in which a temporary negative ion state is formed,... 

For the sake of comparison with the ESCA spectrum of Nj, and to provide a more critical test of the EOM method, we calculate the peak intensities as well as the peak positions. The details of the intensity calculations are left to the Appendix. The dipole approximation is invoked, as the calculation is based on Fermi s golden rule. A plane wave approximation is employed for the outgoing electron. The cross section for the ejected electron is averaged over all possible molecular orientations and polarizations of the incident photon as described by Ellison. ... 

The term %J R)=hlTJ, R) represents the autodetachment lifetime of the anion before the loss of the electron. The parameter o p(E) is defined as the electron capture cross section, which is approximated by... 

Figure 10 Experimental (solid symbols) and theoretical (dashed line, distorted-wave Born approximation full line, Deutsch-Maerk formula and BEB (Binary-Encounter-Bethe) approximation) electron ionization cross section for helium.

Figure 14 Experimental (solid circles and full line) and theoretical K-shell electron ionization cross section for argon dashed line, Born-Bethe approximation dash-dotted line, Deutsch-Maerk formula open circles, Born-Bethe including relativistic corrections.

Using the generalized oscillator strength formulation of the Born approximation, McGuire [6] calculated total electron-ionization cross sections, for elements with 19 2 54. A compilation of experimental data was published in [7]. Experimental values of may include multiple ionization contribution. 

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