Electron and positron scattering from 1,1-C2H2F2

Abstract

1,1-difluoroethylene (1,1-C2H2F2) molecules have been studied for the first time experimentally and theoretically by electron and positron impact. 0.4-1000 eV electron and 0.2-1000 eV positron impact total cross sections (TCSs) were measured using a retarding potential time-of-flight apparatus. In order to probe the resonances observed in the electron TCSs, a crossed-beam method was used to investigate vibrational excitation cross sections over the energy range of 1.3-49 eV and scattering angles 90 degrees and 120 degrees for the two loss energies 0.115 and 0.381 eV corresponding to the dominant C-H (nu2 and nu9) stretching and the combined C-F (nu3) stretching and CH2 (nu11) rocking vibrations, respectively. Electron impact elastic integral cross sections are also reported for calculations carried out using the Schwinger multichannel method with pseudopotentials for the energy range from 0.5 to 50 eV in the static-exchange approximation and from 0.5 to 20 eV in the static-exchange plus polarization approximation. Resonance peaks observed centered at about 2.3, 6.5, and 16 eV in the TCSs have been shown to be mainly due to the vibrational and elastic channels, and assigned to the B2, B1, and A1 symmetries, respectively. The pi* resonance peak at 1.8 eV in C2H4 is observed shifted to 2.3 eV in 1,1-C2H2F2 and to 2.5 eV in C2F4; a phenomenon attributed to the decreasing C=C bond length from C2H4 to C2F4. For positron impact a conspicuous peak is observed below the positronium formation threshold at about 1 eV, and other less pronounced ones centered at about 5 and 20 eV.

Elastic Positron Collisions with 1,1-Difluoroethylene

“…This difference in the signs of the potential makes the positron calculation a more challenging task when compared to electron scattering. Our present calculated ICS is compared with the previous experimental TCS from Makochekanwa et al Additionally, we compare our current data with theoretical and experimental data for the ethylene (C 2 H 4 ) molecule reported by Bettega et al and Sueoka and Mori …”

“…The C 2 H 2 F 2 ICSs, with and without the Born-closure correction, are shown in Figure , alongside the experimental TCSs results measured by Makochekanwa et al The vertical arrow in Figure indicates the positronium formation threshold ( E Ps ), which can be estimated by E Ps = IP – 6.8 eV, where IP is the first ionization potential. For 1,1-difluoroethylene, the experimental value of the first IP is 10.29 eV, which gives E Ps = 3.49 eV.…”

“…In particular, as far as we know, the only study on scattering of positrons by 1,1-difluoroethylene available is from 2007, carried out by Makochekanwa et al The authors reported both electron and positron cross sections for impact energies up to 1000 eV. Besides the electron and positron total cross sections (TCSs), Makochekanwa et al also provided an insightful discussion of their theoretical and experimental results for electron-C 2 H 2 F 2 scattering in close comparison with available data for C 2 H 4 and C 2 F 4 , aiming to understand whether the scattering dynamics is dominated by the ethylene or the perfluoroethylene.…”

“…Nevertheless, these molecules represent a series of greenhouse gases with high global warming potential because of their long lifetimes in the atmosphere . Seeking to reduce global warming emissions, the 1,1-difluoroethylene (C 2 H 2 F 2 , Figure ) molecule has been proposed as a safer candidate to replace perfluorocarbons in industrial applications . Even though plasma process modeling usually requires electron–molecule cross section, the work conducted by Nyffenegger-Pere and Cocks is noteworthy, which used positron beams to obtain some important information on low-temperature plasmas, such as ionization fraction and electron temperature in the bulk of the plasma.…”

“…In this work, we conducted a theoretical study of positron collisions with the 1,1-difluoroethylene molecule. This molecule presents a permanent electric dipole moment (μ = 1.38 D) and molecular polarizability of α = 5.01 Å 3 , which are important parameters in positron–molecule scattering. , The present integral (ICSs) and differential cross sections (DCSs) were obtained employing the Schwinger multichannel method (SMC), in the static plus polarization (SP) approximation, at impact energies up to 10 eV. A correct description of the attractive polarization potential is crucial in positron scattering since the static potential experienced by the positron is repulsive.…”