ELECTRON-PHOTON COINCIDENCE STUDIES OF THE RESOLVED ARGON RESONANCE LINES

The excitation by electron impact at 50 eV, of the 104.8 and 106.7 nm lines of Ar, have been studied separately using the electron-polarised-photon coincidence technique. Polarisation correlations have been measured for electron scattering angles of 0 and 5 degrees . From the measurements at 5 degrees the authors derived the parameters lambda (0.72+or-0.06, 0.60+or-0.05) and mod chi mod (0.99 rad+or-0.19, 0.0) for the 104.8 and 106.7 nm lines, respectively. Thus, contrary to the assumptions of Arriola et al. (see ibid., vol.8, p.1275 (1975)) significant differences may occur between the two lines. The value of chi obtained for the 106.7 nm line implies total coherence at the energy and angle studied. The measurements at 0 degrees yielded 'threshold' polarisations of 0.41+or-0.13 (104.8 nm) and 0.94+or-0.14 (106.7 nm).