Abstract
The electrical strength of a molecule is a measure of its ability to act as an insulator and to absorb electrons. SF6 is a high electric strength gas. This work tries to explain why molecules like SF6 have a high electrical strength from the perspective of electron molecule scattering. The presence of a very low energy (<<1 eV) totally symmetric state in form of a very low-lying resonance, virtual state or very weakly bound state appears to be crucial. R-matrix calculations performed at the static exchange plus polarisation (SEP) level are performed for a number of molecules that show a range of electrical strengths. SEP calculations suggest that SF6 has a strong low energy 2A g resonance feature which becomes a weakly bound state as more virtual orbitals are included in the calculation. High electrical strength molecules such as CCl4, CCl3F and CCl2F2 also have a totally-symmetric low-energy resonance, while the low electrical strength molecules such as CH4, CH3F…CF4 and CClF3, do not show any resonance behaviour in the low energy region. It is suggested that this low energy feature can be used as an indicator when searching for new molecules with high electrical strength facilitating searches for new gases which could provide an alternative to SF6.
Highlights
The electrical strength provides a measure of the ability of a gas to act as an electrical insulator
The results of SF6 and CCl2F2 in this work are higher than the previous results at energies above 0.1 eV, it can be still found that the cross sections of these high electrical strength molecules have high values as the electron energy tends to 0 eV
Elastic cross sections and eigenphases are computed for SF6 and our sample molecules using the static exchange plus polarisation (SEP) model with different numbers of virtual orbitals (VOs) included in the calculation
Summary
The electrical strength provides a measure of the ability of a gas to act as an electrical insulator. This means that there is still a requirement to identify good insulating gases with low GWP (global warming potential) For this purpose, methods of numerically predicting the gas electrical strength have been developed (Rabie et al 2013, Wu et al 2017, Yu et al 2017, Rabie and Franck 2018). Methods of numerically predicting the gas electrical strength have been developed (Rabie et al 2013, Wu et al 2017, Yu et al 2017, Rabie and Franck 2018) Far these methods have largely focussed on target properties such as polarisability and electronegativity but have not considered electron-collision behaviour. We study the relationship between resonances and molecular electrical strength with the hope that this property can be used as indicator of SF6 alternative gases For this we studied ten sample molecules which are listed in table 1.
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