High-resolution energy and angular correlations of the scattered and ejected electrons in electron impact ionisation of argon atoms

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Abstract
The electron impact ionisation (e, 2e) spectrum of argon has been studied with a resultant energy resolution of 0.06 eV and an angular resolution of two degrees in a crossed electron beam and modulated atom beam apparatus. The previously observed 3s3p6, 3s23p43d and 4d(2S1/2) states were identified; the spin-orbit splitting of 0.18 eV between the 3p3/2 and 3p1/2 states was revealed and the 3s23p44s(2P0) state was seen. Angular correlations between the scattered and ejected electrons in coplanar symmetric scattering were obtained for each of the above six states. The deduced electron momentum distributions for these states are consistent with the factorised distorted-wave impulse approximation model formulated by McCarthy and Weigold (1976). The characteristic electron orbitals are those appropriate for the total angular momentum and parity for each state. The cross sections for production of the 3p3/2 and 3p1/2 states are in the ratio of their statistical weights.