Electron scattering from C₄H₆and C₄F₆molecules

Abstract

Absolute electron-impact total cross sections (TCSs) for C 4 H 6 isomers (1, 3butadiene and 2-butyne) and for hexafluoro-2-butyne (C 4 F 6) have been measured in a linear electron-beam transmission experiment as a function of impact energy, between 0.5 and 370 eV. For the C 4 H 6 molecule distinct differences in the shape and magnitude of TCS energy dependences of both isomers are apparent at low energies. In the 1, 3-butadiene TCS curve, the enhancement below 1.2 eV, the narrow maximum centred around 3.2 eV and the dominant broad peak at 9-9.5 eV are easily distinguishable; a very weak shoulder is located near 8 eV. The TCS energy function of 2-butyne demonstrates a remarkable resonant-like maximum located near 3.6 eV and much broader enhancement centred at 8 eV. Above 50 eV both C 4 H 6 curves merge together. The hexafluoro-2-butyne TCS has the maximum near 8 eV and very broad enhancement spanning between 20 and 80 eV; weak shoulders near 3 and 6 eV are also noticeable. The effect of perfluorination is indicated.

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

“…IV C. The previous electron scattering data, 4, 5 reported a shoulder in the TCS between 2.5 and 4.0 eV and peaking somehow at 2.8-3.0 eV, which may also partly be attributed to a resonant electron capture. 20 Around 8 eV, the TCS is characterised by a pronounced maximum 4,5 and we notice in a recent study on the electronic state spectroscopy of the C 4 F 6 isomers 1 that hexafluoro-2-butyne shows an intense oscillator strength (at 9.94 eV) assigned to the A 2u component of the π (6e u ) → π * (6e g ) transition.…”

“…The latter was reported in other perfluorinated hydrocarbons and attributed to a behaviour in common with perfluorinated compounds. 4,5 This is particularly relevant for discussion in Sec. IV C. The previous electron scattering data, 4, 5 reported a shoulder in the TCS between 2.5 and 4.0 eV and peaking somehow at 2.8-3.0 eV, which may also partly be attributed to a resonant electron capture.…”

“…In contrast to 1,3-C 4 F 6 , Szmytkowski and Kwitnewski 4,5 noticed that the TCS of 2-C 4 F 6 does not show a maximum at very low energies but only one very broad enhancement with two maxima peaking at ∼8 and 30 eV. The latter was reported in other perfluorinated hydrocarbons and attributed to a behaviour in common with perfluorinated compounds.…”

“…This may be related to several weak resonant channels opening in this energy range as can be seen on the rising slope of the broad feature at about 5 and 8 eV in the TCS. 4,5 From these, the former may be related to the formation of TNIs, i.e., the temporary trapping of the incident electron in a π a (20a) → π b * (20b) antibonding molecular orbital, observed in the electron spectra, 1,22 and the latter with higher lying resonances from dissociative electron attachment experiments. 20,21 At higher energies, the experimental data agrees well with the IAM-SCAR calculation which is reminiscent of the dominant direct scattering in this energy range.…”

Electron collisons with cyclobutane

“…In the last three years, motivated by some experimental works [1][2][3][4], we have been investigating electron collisions with isomers of small hydrocarbons, focusing on the isomer effect. This effect allows one to distinguish the different isomers of a molecule by differences in their cross sections.…”