Absolute cross sections for electron-impact ionization of the rare-gas atoms by the fast-neutral-beam method

A new apparatus has been constructed for the measurement of absolute partial electron-impact-ionization cross sections of neutral atoms, molecules, and free radicals. A fast neutral beam is prepared by charge-transfer neutralization of a mass-selected ion beam and is ionized as it crosses an electron beam. From careful analysis of the apparatus, the absolute accuracy of measured cross sections is calculated to be +/-12%. Combined with statistical errors, this gives about +/-15% for the overall accuracy. Measurements of ionization cross sections for the four rare gases He, Ne, Ar, and Kr from 0 to 200 eV agree with the most reliable previous values within +/-6%. The measured Xe ionization cross section is 12% greater than the previous best value. Ratios of double- and triple-ionization to single-ionization cross sections for Ar, Kr, and Xe confirm the recent measurements of Stephan, Helm, and Märk [J. Chem. Phys. 73, 3763 (1980)].