Electron impact multiple ionization of neon, argon and xenon atoms close, to threshold:: appearance energies and Wannier exponents

We report the results of the experimental determination of the appearance energy values AE(Xn+/X) for the formation of multiply charged Ne, Ar and Xe ions up to n = 4 (Ne), n = 6 (Ar) and n = 8 (Xe) following electron impact on Ne, Ar and Xe atoms using a dedicated high-resolution electron impact ionization mass spectrometer. The data analysis uses the Marquart-Levenberg algorithm, which is an iterative, nonlinear least-squares-fitting routine, in conjunction with either a two-function or a three-function fit based on a power threshold law. This allows us to extract the relevant AEs and corresponding exponents for a Wannier-type power law from the measured near-threshold data. The values of the AEs determined in this work are compared with other available experimental and spectroscopic values of the AEs,and the extracted-exponents are compared with other available experimental data and with the predictions of the various Wannier-type power law models.