Three-dimensional images for electron-impact single ionization of He: complete and comprehensive (e, 2e) benchmark data

Strong molecular alignment dependence of H2 electron impact ionization dynamics

Low-energy (E(0) = 54 eV) electron impact single ionization of molecular hydrogen (H(2)) has been investigated as a function of molecular alignment in order to benchmark recent theoretical predictions [Colgan et al., Phys. Rev. Lett. 101, 233201 (2008) and Al-Hagan et al., Nature Phys. 5, 59 (2009)]. In contrast to any previous work, we observe distinct alignment dependence of the (e,2e) cross sections in the perpendicular plane in good overall agreement with results from time-dependent close-coupling calculations. The cross section behavior can be consistently explained by a rescattering of the ejected electron in the molecular potential resulting in an effective focusing along the molecular axis.

Out-of-plane (e, 2e) experiments on helium L=0, 1, 2 autoionizing levels

Out-of-plane (e, 2e) measurements are reported for the helium autoionizing levels (2s2)1S, (2p2)1D, (2s2p)1P, and for direct ionization. While the recoil peak almost vanishes in the angular distribution for direct ionization, it remains significant for the autoionizing levels and exhibits a characteristic shape for each orbital angular momentum L=0, 1, 2. A second-order model in the projectile-target interaction correctly reproduces the observed magnitudes of the recoil peaks, but is a factor of 2 too large in the central out-of-plane region.