Electron-impact excitation of argon: II. The lowest resonance 4s[3/2]1and metastable 4s[3/2]2and 4s'[½]0states

Absolute normalized differential electron-impact excitation cross sections (DCSs) are presented for the lowest three electronic states of argon: the lowest resonance 4s[ 3 / 2 ] 1 (1s 4 in Paschen's notation) state and two neighbouring metastable 4s[ 3 / 2 ] 2 and 4s'[½] 0 (1s 5 and 1s 3 in Paschen's notation) states. Direct, i.e. free of a cascade contribution, excitation cross sections were obtained experimentally for the 4s[ 3 / 2 ] 1 state at 20, 40, 50 and 80 eV and for the 4s[ 3 / 2 ] 2 and 4s'[½] 0 states at 20 and 40 eV impact energies. The measurements were performed at scattering angles between 5° and 150° with an angular resolution of better than 2°. The ratios: r = DCS(4s[ 3 / 2 ] 2 )/DCS(4s'[½] 0 ) and r ' = DCS(4s[ 3 / 2 ] 1 )/DCS(4s'[½] 1 ) were determined and compared with other available experimental and theoretical results. The absolute DCS scale was established with respect to DCSs of the 4s'[½] 1 state ( Filipovic et al 2000 J. Phys. B: At. Mol. Opt. Phys. 33 677 ) using the peak intensity ratios in the energy-loss spectra. The DCSs were extrapolated to 0° and 180° and numerically integrated to yield integral, momentum transfer and viscosity cross sections.