ABSOLUTE PARTIAL AND TOTAL CROSS-SECTIONS FOR ELECTRON-IMPACT IONIZATION OF ARGON FROM THRESHOLD TO 1000 EV

Absolute partial cross sections from threshold to 1000 eV are reported for the production of Ar-n+ (n = 1-4) by electron-impact ionization of argon. The total cross sections, obtained from an appropriately weighted sum of the partial cross sections, are also reported. These results are obtained with an apparatus incorporating a time-of-flight mass spectrometer with position-sensitive detection of the product ions. The simple apparatus design embodies recent developments in pressure measurement and particle detection and is believed to yield more reliable results than those previously reported. For singly charged ions, the overall uncertainty in the absolute cross section values reported here is +/-3.5%. Previous measurements of absolute partial and total cross sections are reviewed and compared with the present results.