Remarks on total and elastic cross sections for electron and positron scattering from CO2

Abstract

There remain discrepancies in the determination of the total and elastic cross sections for electron and positron collisions with carbon dioxide at impact energies from 0.3 to 100 eV. We have carried out a joint experimental and theoretical study in an attempt to resolve the differences. Our measurements for total cross sections for electron impact agree extremely well with those of Hoffman et al. ͓Phys. Rev. A 25, 1393 ͑1982͔͒ above 2 eV, while those for positron impact agree to better than 15% in magnitude, and are in an excellent accord for the energy-dependence. The present observations, along with an analysis using a knowledge of the dominant inelastic processes, lead us to conclude that the total cross section determined in earlier studies is a considerable underestimate at intermediate energies, where inelastic processes are not negligible. The analysis provides a rationale for understanding the discrepancies. Furthermore, we present that the total cross section by positron impact below 2 eV becomes larger by 20% than that of electron impact, and provide a rationale as well as implication to a possible application.

Mode Dependence in Vibrational Excitation of aCO2Molecule by Electron and Positron Impacts

“…For specific inelastic processes, unfortunately, very few systematic studies by e 1 impact have been performed for gaseous targets, and a detailed comparative study between e 2 and e 1 impact is virtually nonexistent except for some preliminary investigation of experimental results for raregas atoms and simple molecules [2]. Only recently, Gianturco and colleagues [3(a)] have carried out a careful study on e 1 scattering from CO 2 molecule for elastic as well as vibrational excitation processes for the symmetric stretching mode, and have compared it with their previous study [3(b)] for e 2 scattering in order to shed some light on the coupling mechanism.Earlier in our study [4], we have observed that the total cross section for CO 2 for e 2 impact is indeed larger by 40% than that for e 1 impact below 100 eV or so, and continues to be so until the impact energy reaches down to 3 eV. Below 3 eV, however, the magnitude of the cross section is found to reverse, i.e., the total cross section for e 1 impact becomes larger by 25%, although it reverses again at much lower energy around 0.5 eV.…”

“…Earlier in our study [4], we have observed that the total cross section for CO 2 for e 2 impact is indeed larger by 40% than that for e 1 impact below 100 eV or so, and continues to be so until the impact energy reaches down to 3 eV. Below 3 eV, however, the magnitude of the cross section is found to reverse, i.e., the total cross section for e 1 impact becomes larger by 25%, although it reverses again at much lower energy around 0.5 eV.…”

Monte Carlo model of electron energy degradation in a CO2 atmosphere

“…The laboratory measured total scattering cross section (TCS) is available between 0.1 eV and 5000 eV. The TCS for e‐CO 2 collision has been measured by several authors in different energy ranges: Ferch et al [1981] in the energy range 0.007–4.5 eV, Buckman et al [1987] 0.1–5 eV, Szmytkowski et al [1987] 0.5–3000 eV, Kimura et al [1997] 0.8–500 eV, Kwan et al [1983] 1–500 eV, and Garcia and Manero [1996] 400–5000 eV. At low energies, the TCS of Szmytkowski et al [1987], Buckman et al [1987], and Ferch et al [1981] are in agreement to within 10%.…”

“…In the lowest energy range (<1 eV) Zecca et al [2002] adopted the experimental data of Ferch et al [1981] and Buckman et al [1987], which are in good agreement with each other. In the 1–1000 eV energy range, Zecca et al [2002] averaged the cross sections obtained by Szmytkowski et al [1987], Kimura et al [1997], and Kwan et al [1983], with equal weight, to obtain the recommended values, which are in good agreement with Garcia and Manero [1996] at higher (>400 eV) energies. In his review, Itikawa [2002] has recommended the TCS of Zecca et al [2002].…”

Modified effective range analysis of low energy electron and positron scattering on CO2

“…First measurements by Sueoka and collaborators [19] were performed down to 1 eV using 67.5 mm long scattering cell (we quote the geometrical length and not the "effective" 79.7 mm length) with 4 mm radius apertures and 9 G guiding field. The more recent data [20] (quoted also in [21]) were performed down to 0.3 eV with 1.8 G guiding field and 3 mm radius apertures; at 1 eV those data are by 10% lower than the value of Kwan et al [22] and 20% higher than the early set [19].…”