Low-energy electron scattering from halomethanes. I. Elastic differential cross section for e-CF₄scattering

Abstract

In a crossed-beam experiment, the authors have studied vibrationally elastic and inelastic scattering of electrons by CF4 in the energy range 0.3-20 eV. The angular range covered by the measurements is from 10' to 105'. In the present paper, they report their results for elastic scattering. Absolute values of the differential cross section (DCS) are determined with reference to the total cross section measured by Jones (1986). For energies above 10 eV, the experimental results are well described by the 'static-exchange' multichannel Schwinger variational principle (SMC) calculations of Huo (1988). At lower energies, the measurements show strong deviations from the calculated results which are attributed to neglect of the polarization effects in the calculations. The elastic e-CF4 scattering shows a Ramsauer-Townsend effect below E=0.5 eV. The data have been evaluated by means of a modified effective range theory (MERT) analysis, and the resulting integral cross sections are compared with results from swarm experiments.

Low-energy electron scattering by C2HF5

“…1 is artifactual. It is also important to note that, in the related fluorocarbon CF 4 , similar resonant peaks are seen in the fixed-nuclei elastic cross sections computed by various methods, [28][29][30][31] but not in the measured vibrationally elastic cross section; 32,33 rather, in CF 4 one finds strong resonant enhancement of the vibrationally inelastic cross sections 32,34 in the relevant energy range. We therefore speculate that much, if not most of the resonant enhancement of the C 2 HF 5 FN elastic cross section, may likewise contribute to vibrational excitation.…”

Low-energy elastic electron scattering by tetrafluoromethane (CF4)

“…4 and 5, we show differential cross sections at selected energies, together with experimental results. 10,11 As is generally true for static-exchange calculations, the differential cross section is qualitatively incorrect at low energies but quite accurate at higher energies. From the differential cross sections, we obtain the momentumtransfer cross section, shown in Fig.…”

Analytic approach to modified effective-range theory for electron and positron elastic scattering

“…Due to its simplicity MERT has gained considerable popularity and has been frequently used to extrapolate measured cross sections to the very low energy range and very small scattering angles that are inaccessible experimentally [10][11][12][13]. In the standard approach the extrapolation relies on the effective-range expansion of scattering phase shifts of partial waves in powers of the projectile momentum k. An intrinsic drawback of such a procedure is the quick divergence of the k series with rising energy.…”