(e,2e) Studies of Atoms ? Some Recent Developments

Abstract

Some recent work on (e,2e) collisions in atoms is reported. The first (e,2e) results on an excited target and also on an oriented target are discussed. Sodium atoms are pumped to the m/ = +1 state of the excited 3p state by 0"+ light from a laser. The (e,2e) measurements are then performed on this excited state. The results are in excellent agreement with the momentum density profile given by the 3p(m/ = 1) Hartree-Fock wavefunction. High resolution electron momentum spectroscopy measurements are reported for argon. The first momentum profiles for excited Ar ion states belonging to the 2po and 20e manifolds are obtained. The latter are entirely due to initial state correlations. Comparison is made with several many-body calculations. The importance of core quadrupole (10) excitations is demonstrated. Although the 2se manifold is dominated by final state correlations, the momentum profile to the 4s 2S ion state in the 2Se manifold also shows the influenee of initial state correlation effects. The third series of measurements examines correlations in the autoionising region of helium, encompassing the (2s2)1 S, (2s2p)3p, (2p2)! 0 and (2s2p)! P resonances, at 100, 200 and 400 eV incident electron energies. Measurements, with an energy resolution of 150 meV, were taken at a number of scattered electron angles over an extended range of ejected electron angles, encompassing both the binary and recoil regions. The data show very strong correlations between the resonance amplitudes and the direct ionisation amplitudes.