Triple differential cross section of single Ar(2p) ionization by electron impact in the keV region

Angular correlation measurements of the two final electrons following primary ionization of the Ar(2p) orbital are performed at 2 keV and 3 keV in a wide range of momentum transfer revealing a strong dependence of structural parameters on the kinematical conditions. Characteristic features are a dominant recoil structure at small momentum transfer, a breaking of symmetry around the direction of momentum transfer and a deviation of the recoil peak maximum from the axis of momentum transfer towards smaller deflection angles. The electron momentum density of the Ar(2p) orbital was extracted out of experimental data for the first time. Within experimental errors good agreement was found with results of Hartree-Fock calculations. Extension of the technique of electron momentum spectroscopy performed in slightly asymmetric coplanar kinematics to study electronic structure has been achieved.