Electron impact double ionisation of Ar+and Ar4+ions

Employing an improved crossed-beam technique described in the preceding paper, cross sections sigma q,q+2 for electron impact double ionisation of Ar q+ ions (q=1 and q=4) were measured for electron energies from threshold to about 700 eV. The improved experimental accuracy allowed contributions of L-shell ionisation-autoionisation to sigma 1,3 to be identified for Ar + . With increasing q the relative importance of the L-shell contribution to sigma q,q+2 strongly increases. As a result the cross section sigma 4,6 for Ar 4+ is by far dominated by the L-shell contribution at energies above 350 eV. Calculations on the basis of semiempirical and semiclassical theories are made to compare the relative strengths of direct double ionisation and inner-shell ionisation with subsequent electron emission.