Total cross sections for low and intermediate energy positrons and electrons colliding with CH₄, C₂H₄and C₂H₆molecules

Positron collisions with ethene

“…We see good accord between the present measurements and those of Floeder et al [8], within the combined total error bars (not plotted), even down to 5 eV. However, the present data and that of Sueoka and Mori [9] differ considerably at smaller energies (<7 eV), where our data presents a sharp increase in magnitude when compared to that earlier measurement. We believe that this discrepancy is mainly due to the different angular discrimination (which is energy dependent) of the experiments.…”

“…Although the experimental data agree relatively well for energies above ∼7 eV, they differ in magnitude for lower energies. Previous calculations reported by da Silva et al [10,13] pointed out the existence of a Ramsauer-Townsend minimum around 2 eV, and were in good agreement with the experimental data available at the time [9]. Occhigrossi and Gianturco [12] also reported elastic integral cross sections and annihilation parameter (Z eff ) estimates for positron collisions with ethene, although they did not discuss the Ramsauer-Townsend minimum.…”

“…3 shows our present experimental TCS and theoretical elastic ICS in comparison with the data from Sueoka and Mori [9] and from Floeder et al [8], as well as calculations from Sun et al [11], da Silva et al [10], and of Occhigrossi and Gianturco [12]. In this figure the threshold for positronium formation (P s ) of 3.7 eV and the first ionization potential (IP) of 10.5 eV [32] are indicated by vertical arrows.…”

“…They originate from the quadrature combination of quantities like the statistical uncertainties, the uncertainty in the thermal transpiration corrections (<2%), the uncertainty in the value of the length of the scattering region and its correction for the effective positron path length (<3%), and the uncertainties in the pressure and temperature readings (<1% each). [8]; squares (red), results from [9]; dot-dashed line (magenta), ICS from [10]; dashed line (orange), ICS from [12]. (Lower panel) Same as top panel, in a smaller scale, except that here we have also, at 0.1, 0.5, 1, 5, and 10 eV, included the present TCSs corrected for the forward angle scattering effect (using our theoretical differential cross sections), open circles (black).…”

“…There are also experimental [8,9] and theoretical [10][11][12][13] studies addressing positron collisions with ethene. Although the experimental data agree relatively well for energies above ∼7 eV, they differ in magnitude for lower energies.…”