Abstract
There are many measurements and calculations of total electron impact ionisation cross sections. However, many applications, particularly in plasma physics, also require fragmentation patterns. Approximate methods of deducing partial cross sections are tested based on the use of total cross section computed within the well-used binary encounter Bethe approximation. Partial ionisation cross sections for three series of molecules including CH4, CF4 and CCl4; SiH4 and SiCl4; NH3 and PH3, were estimated using two methods. Method one is semi-empirical and uses mass spectroscopy data to fix the partial cross sections at a single electron energy. The second is a fully computational method proposed by Huber et al (2019 J. Chem. Phys. 150 024306). Comparisons with experimental results suggest that the mass spectroscopy method is more accurate. However, as Huber’s method requires no experimental input, this method could be used as a first approximation when no experimental data is available. As mass spectroscopy sometimes provides incomplete datasets, a hybrid method based on the use of both methods is also explored.
Highlights
Electron impact ionisation cross sections have importance in many areas of science including cri pt astrophysics and astrochemistry[1 ], plasma sciences[2,3,4,5] and environmental sciences6,7
A number of empirically motivated models are available for predicting total ionisation cross sections such as the Binary Encounter Bethe (BEB) method proposed by Kim and Rudd[8 ], the Deutsch-Märk[9] (DM) method and the Spherical Complex Optical Potential[10] (SCOP) method
Effective Core Potential (ECP) can improve the description of relativistic effects in heavy atoms, which in turn improve the representation of the valence orbitals
Summary
Electron impact ionisation cross sections have importance in many areas of science including cri pt astrophysics and astrochemistry[1 ], plasma sciences[2,3,4,5] and environmental sciences. A number of empirically motivated models are available for predicting total ionisation cross sections such as the Binary Encounter Bethe (BEB) method proposed by Kim and Rudd[8 ], the Deutsch-Märk[9] (DM) method and the Spherical Complex Optical Potential[10] (SCOP) method. These have been extensively used to calculate the total ionisation cross sections of atoms, molecules, ions, radicals and clusters with generally us successful outcomes.[11,12] In a previous paper by the authors[13] improvements to the computational total cross section using the BEB method were investigated by using Effective Core Potential (ECP) basis sets as well as using a semi-empirical polarizability scaling factor, α BEB. Use of an ECP means the iondM isation of the inner electrons is no longer modelled, resulting in an underestimation of ionisation cross sections at high energy
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