Out-of-plane (e,2e) measurements and calculations on He autoionizing levels as a function of incident-electron energy

Out-of-scattering-plane (e,2e) measurements and calculations are reported for the three singlet helium 2 2 ′ autoionizing levels, with 80, 100, 120, 150, and 488 eV incident-electron energies, and scattering angles 60, 50.8, 45, 39.2, and 20.5, respectively. The kinematics are the same in all cases: the momentum transfer is K=2.1 a.u., and ejected electrons are detected in a plane that contains the momentum-transfer direction and is perpendicular to the scattering plane. The results are presented as (e,2e) angular distributions energy integrated over each level. They are compared with fully nonperturbative B-spline R-matrix and hybrid second-order distorted-wave + R-matrix calculations.