Cross sections for elastic scattering of electrons by CF3Cl, CF2Cl2, and CFCl3

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Isomerism is ubiquitous in chemistry, physics, and biology. In atomic and molecular physics, in particular, isomer effects are well known in electron-impact phenomena; however, very little is known for positron collisions. Here we report on a set of experimental and theoretical cross sections for low-energy positron scattering from the three structural isomers of pentane: normal-pentane, isopentane, and neopentane. Total cross sections for positron scattering from normal-pentane and isopentane were measured at the University of Trento at incident energies between 0.1 and 50 eV. Calculations of the total cross sections, integral cross sections for elastic scattering, positronium formation, and electronic excitations plus direct ionization, as well as elastic differential cross sections were computed for all three isomers between 1 and 1000 eV using the independent atom model with screening corrected additivity rule. No definitive evidence of a significant isomer effect in positron scattering from the pentane isomers appears to be present.

Section: E Comparison Of the Homologous Series Of Molecules C N H 2n+2supporting

confidence: 90%

Experimental and theoretical cross sections for positron scattering from the pentane isomers

Chiari

Zecca

Blanco

et al. 2016

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“…The independent atom model with screening corrected additivity rule (IAM-SCAR) method has had significant use in calculating electron scattering cross sections for a wide variety of molecular targets (see, e.g., Refs. [21][22][23][24][25][26] and over a broad energy (E 0 ) range (typically ∼1-5000 eV). As a consequence, we only précis the key points of that approach here.…”

Section: Atomic Optical Model (Om)mentioning

confidence: 99%

Electron collisions with phenol: Total, integral, differential, and momentum transfer cross sections and the role of multichannel coupling effects on the elastic channel

Costa

Oliveira

Bettega

et al. 2015

We report theoretical and experimental total cross sections for electron scattering by phenol (C6H5OH). The experimental data were obtained with an apparatus based in Madrid and the calculated cross sections with two different methodologies, the independent atom method with screening corrected additivity rule (IAM-SCAR), and the Schwinger multichannel method with pseudopotentials (SMCPP). The SMCPP method in the Nopen-channel coupling scheme, at the static-exchange-plus-polarization approximation, is employed to calculate the scattering amplitudes at impact energies ranging from 5.0 eV to 50 eV. We discuss the multichannel coupling effects in the calculated cross sections, in particular how the number of excited states included in the open-channel space impacts upon the convergence of the elastic cross sections at higher collision energies. The IAM-SCAR approach was also used to obtain the elastic differential cross sections (DCSs) and for correcting the experimental total cross sections for the so-called forward angle scattering effect. We found a very good agreement between our SMCPP theoretical differential, integral, and momentum transfer cross sections and experimental data for benzene (a molecule differing from phenol by replacing a hydrogen atom in benzene with a hydroxyl group). Although some discrepancies were found for lower energies, the agreement between the SMCPP data and the DCSs obtained with the IAM-SCAR method improves, as expected, as the impact energy increases. We also have a good agreement among the present SMCPP calculated total cross section (which includes elastic, 32 inelastic electronic excitation processes and ionization contributions, the latter estimated with the binary-encounter-Bethe model), the IAM-SCAR total cross section, and the experimental data when the latter is corrected for the forward angle scattering effect [Fuss et al., Phys. Rev. A 88, 042702 (2013)].

“…The effect of the SCAR corrections is to reduce the contribution of the atomic cross sections when they overlap (i.e., at the lower energies). This approximation has been, however, applied successfully: (1) if the constituent atoms in the target are heavy atoms 23 and (2) if the interaction region is the inner part of each atom for fast electrons large-angle scattering, 7 where the potential field is more or less spherical. Even so, at 200 eV for C 4 F 6 isomers, some deviations are emerging commonly for backward scattering above 90 • , which may be due to the multiple scattering processes in a molecule.…”

Section: A Elastic Dcs Overviewmentioning

confidence: 99%

“…This has allowed us to suggest strong evidence in support of the assertion that atomic-like effects may remain prevalent in what are fundamentally molecular systems. Moreover, Hoshino et al 23 as a result of progressively substituting a Cl-atom in going from CF 4 to CF 3 Cl to CF 2 Cl 2 to CFCl 3 , and to CCl 4 , the undulations in the angular distributions have been found to vary in a largely systematic manner, concluding therefore that the elastic scattering process is dominated by the atomic-Cl atoms of the molecules.…”

Section: B Comparison With the Atomic F-dcsmentioning

confidence: 99%

Elastic differential cross sections for C4F6 isomers in the 1.5–200 eV energy electron impact: Similarities with six fluorine containing molecules and evidence of F-atom like scattering

Hoshino

Limão‐Vieira

Anzai

et al. 2014

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We report absolute elastic differential cross sections for electron interactions with the C 4 F 6 isomers, hexafluoro-1,3-butadiene (1,3-C 4 F 6 ), hexafluoro-2-butyne (2-C 4 F 6 ), and hexafluorocyclobutene (c-C 4 F 6 ). The incident electron energy range is 1.5-200 eV, and the scattered electron angular range for the differential measurements varies from 15 • to 150 • . In all cases the absolute scale of the differential cross section was set using the relative flow technique, with helium as the reference species. Atomic-like behaviour in these scattering systems is shown here for the first time, and is further investigated by comparing the elastic cross sections for the C 4 F 6 isomers with other fluorinated molecules, such as SF 6 and C n F 6 (n = 2, 3, and 6). We note that for all the six-F containing molecules, the scattering process for electron energies above 30 eV is indistinguishable. Finally, we report results for calculations of elastic differential cross sections for electron scattering from each of these isomers, within an optical potential method and assuming a screened corrected independent atom representation. The level of agreement between these calculations and our measurements is found to be quite remarkable in all cases.