Calculation of postionization probabilities as a function of plasma parameters in electron gas secondary neutral mass spectrometry

Using the semiempirical cross‐section functions for electron impact ionization developed by Lotz, we calculated the ionization rate constants for most elements as a function of the electron temperature in a low‐pressure noble gas plasma typically employed in electron gas secondary neutral mass spectrometry (SNMS). After first‐order corrections accounting for (a) the different mean energies of sputtered neutral particles and (b) signal losses due to heavy particle scattering by discharge gas particles (e.g., Ar), the neutral‐to‐ion conversion factors α⁰_X are calculated for the Leybold INA 3 system for most elements X across the Periodic Table. Assuming uniform (mass independent) transmission in the detection system the ratios α⁰_Fe/α⁰_X are equivalent with the relative sensitivity factors D⁰_Fe/D⁰_X in SNMS.