Mass spectrometric determination of partial electron impact ionization cross sections of He, Ne, Ar and Kr from threshold up to 180 eV

TLDR

The study addresses challenges in ion extraction from a Nier‑type source and ion transmission through a double‑focusing Varian MAT CH5 mass spectrometer. Partial cross section ratios were summed, weighted by charge number, to obtain relative total ionization cross sections for each gas. Using a novel mass‑spectrometric approach, the authors measured accurate relative partial ionization cross sections for He, Ne, Ar, and Kr up to 180 eV, derived absolute values by normalizing to ionization‑tube data, and found good agreement with previous measurements.

Abstract

A new approach to mass spectrometric measurement and analysis has been used to study the electron impact ionization of the rare gases in the low electron energy regime (<180 eV). Critical considerations are given to the problems of ion extraction from the ion source (Nier-type) and the transmission of the extracted ions through the mass spectrometer system (double focusing sector field Varian MAT CH5). Accurate relative partial cross section functions were obtained for production of He+ and He2+ from He; Ne+, Ne2+, and Ne3+ from Ne; Ar+, Ar2+, Ar3+ from Ar, and Kr+, Kr2+, Kr3+ and Kr4+ from Kr. In addition, the cross section ratios for the partial ionization cross sections of each individual gas were determined. These ratios were used to sum up the relative partial cross section functions for each gas, hence obtaining relative total ionization cross section functions by weighting each partial cross section function with the respective charge number. The shape of the relative total ionization cross section function thus obtained was compared with ionization tube measurements of the total ionization cross section curve. Good agreement with the data of Rapp and Englander-Golden was found. This comparison allows the normalization of the measured relative partial cross section functions, yielding absolute partial cross section values for all of the processes mentioned above. The experimental results presented are compared with previous determinations where available.