Electron and Positron Scattering Cross Sections from CO₂: A Comparative Study over a Broad Energy Range (0.1–5000 eV)

Abstract

In this Review, we present a comparative study between electron and positron scattering cross sections from CO 2 molecules over a broad impact energy range (0.1–5000 eV). For electron scattering, new total electron scattering cross sections (e-TCS) have been measured with a high resolution magnetically confined electron beam transmission system from 1 to 200 eV. Dissociative electron attachment processes for electron energies from 3 to 52 eV have been analyzed by measuring the relative O – anion production yield. In addition, elastic, inelastic, and total scattering cross section calculations have been carried out in the framework of the Independent Atom Model by using the Screening Corrected Additive Rule, including interference effects (IAM-SCARI). Based on the previous cross section compilation from Itikawa ( J. Phys. Chem. Ref. Data 2002 31 749 767 ) and the present measurements and calculations, an updated recommended e-TCS data set has been used as reference values to obtain a self-consistent integral cross section data set for the elastic and inelastic (vibrational excitation, electronic excitation, and ionization) scattering channels. A similar calculation has been carried out for positrons, which shows important differences between the electron scattering behavior: e.g., more relevance of the target polarization at the lower energies, more efficient excitation of the target at intermediate energies, but a lower total scattering cross section for increasing energies, even at 5000 eV. This result does not agree with the charge independence of the scattering cross section predicted by the first Born approximation (FBA). However, we have shown that the inelastic channels follow the FBA’s predictions for energies above 500 eV while the elastic part, due to the different signs of the scattering potential constituent terms, remains lower for positrons even at the maximum impact energy considered here (5000 eV). As in the case of electrons, a self-consistent set of integral positron scattering cross sections, including elastic and inelastic (vibrational excitation, electronic excitation, positronium formation, and ionization) channels is provided. Again, to derive these data, positron scattering total cross sections based on a previous compilation from Brunger et al. ( J. Phys. Chem. Ref. Data 2017 46 023102 ) and the present calculation have been used as reference values. Data for the main inelastic channels, i.e. direct ionization and positronium formation, derived with this procedure, show excellent agreement with the experimental results available in the literature. Inconsistencies found between different model potential calculations, both for the elastic and inelastic collision processes, suggest that new calculations using more sophisticated methods are required.

Electron- and positron-driven molecular processes for H2O, CO2, and NH3 in their gas and ice phases

“…However, their curve is slightly shifted at the lower energy side but shows very good matching with the present results after the peak value. 8 Except for the peak region, the current results are a good match with the theoretical results of Kumar and Kumar, 34 Patel and Joshipura, 32 and Hwang et al 28 The inelastic cross-sections (Q inel ) for NH 3 are presented in Fig. 5, and show excellent agreement with the experimental data of Homam et al 38 throughout the energy range and are overestimated as compared to the old results reported by Jain 43 using various models.…”

“…6,7 They are essential while investigating chemical reactions, atmospheric phenomena, and the behavior of matter under extreme situations. 8 Electrons (e À ) and positrons (e + ) are complementary particles and possess distinct properties that significantly influence their interaction with molecules. In this study, we explored the electron and positron-driven molecular chemistry of H 2 O, CO 2 , and NH 3 in gas and ice forms.…”

Integral Electron Scattering Cross Sections from N2O for Impact Energies Ranging from 1 to 1000 eV

“…As we mentioned in a recent review on the CO 2 molecule, for the integral elastic, we recommend on the information from the calculations. The combination of accurate “ab initio” low-energy scattering methods with intermediate-high energy model potential calculations provides, in general, integral elastic cross sections with verified uncertainties within 10% (see, e.g., refs and However, experimental integral elastic cross section (IECS) values are derived from the integration of the corresponding differential elastic cross section measurements, which are in general contaminated with the rotational excitation and require theoretical extrapolations to both small and large scattering angles, leading, in general, to higher uncertainty limits (20–25%). In addition, the absolute experimental DCS values require normalization procedures based on relative flow techniques or directly from calculations.…”

“…As already mentioned, from a theoretical point of view, electron attachment cross sections appear as resonances superimposed to the calculated integral elastic cross sections. According to the procedure, we proposed to derive a complete set of inelastic cross sections, the electron attachment cross section is derived by subtracting the integral elastic cross section (once removed the calculated resonances) from the experimental TCS reference values. All the resonant structures around the anion formation peaks reported by Rapp and Briglia and Krishnakumar and Srivastava have been assigned to electron attachment processes.…”

“…As aforementioned, total scattering and ionization cross sections have been calculated with our independent atom with screening corrections and interference effects (IAM-SCAR + I) method. − This is a well-established procedure that has been demonstrated to be reliable within 10%, at impact energies above 20 eV, for a large number of molecular targets, from triatomic to more complex molecules . Hence, we present here the results of this calculation only for impact energies above 10 eV.…”