Mass Spectrometry-Based Approach to Compute Electron-Impact Partial Ionization Cross-Sections of Methane, Water and Nitromethane from Threshold to 5 keV

Abstract

The electron impact partial ionization cross-sections of molecules such as methane, water and nitromethane are computed using a modified form of the binary encounter Bethe (BEB) formula. The modified form of the BEB model works on rescaling the molecular binding energies of the orbitals and the scaling of cross-sections using the electron ionization mass spectrometry data. The computed partial ionization cross-sections are consistent with the recommended data and are better than several experimental and theoretical results. The summed partial ionization cross-sections of different fragments also agree with the total ionization cross-sections obtained from BEB and the experimental data. This work highlights the utility of mass spectrometry in the modeling and interpretation of the ionization cross-section data. The limitations and the advantages of the modified form of the BEB model are also discussed.

Keywords

• electron collision
• ionization cross-sections
• BEB model
• mass spectrometry
• appearance energy
• semi-empirical methods