(e, 2e) ionization differential cross sections are presented for incident electron energies ranging from 15 eV to 95 eV above the ionization threshold of the 1b 1 molecular state of H 2 O. Experimental results and theoretical analysis were derived for three energies in a coplanar symmetric geometry, and for three energies in an asymmetric geometry. The experimental data show a wide variation in the cross section over this range of energies, whereas the theoretical analysis carried out using a sophisticated molecular DWBA model, which includes the final state post collision interaction (PCI), shows best agreement at lower energies. The experimental techniques used to collect the data are described here as well as an improved theoretical approach using elastic scattering cross sections to evaluate the accuracy of the distorted waves utilized in the calculation of the ionization cross sections.

Experimental results are reported for the (e, 2e) differential ionization crosssection from the 3σ g and 1π u valence molecular orbitals of molecular nitrogen N 2 at incident electron energies between 25.6 and 76.7 eV. The measurements have been conducted in a coplanar symmetric geometry in an energy regime where ionization is sensitive to contributions from shape resonances and autoionizing doubly excited states. The results suggest that these additional channels may contribute to the measured cross-section. The measurements also display trends qualitatively similar to previous results at higher incident electron energies using the same geometry.

Gao et al (2005 Phys. Rev. A 72 032721) have predicted a Young's type interference effect in the fully differential cross sections for ionization of the 3σ g state of N 2 for highly asymmetric collisions with one electron detector fixed at very small scattering angles (1 • or 10 •). The purpose of this work was to look for this interference effect at a larger scattering angle. (e, 2e) ionization measurements have been conducted from the 3σ g and 2σ * u states of N 2 in a coplanar asymmetric geometry, where one electron emerges in the forward direction and the correlated electron is measured as a function of scattering angle. Both final-state electrons have an energy of 30 eV, and the forward scattering angle was θ a = 22 • relative to the incident beam direction. The theoretical prediction is that there should be a strong interference peak near 180 •. The measurements were carried out from the 3σ g state over a range of scattering angles from θ b ∼ 10 • to θ b ∼ 170 • using a magnetic angle changing spectrometer. The present experimental results for 3σ g find a normal binary peak plus another peak at back angles in the vicinity of 180 •. Consequently, this work supports the possibility of a strong Young's type interference effect for small fixed scattering angles.

Super-elastic scattering processes can be considered as the 'time reversal' of electron-photon coincidence measurements, with the advantage that data are accumulated thousands of times faster. This allows a far more extensive and accurate study of electron excitation of atoms which can also be excited using laser radiation. The application of a newly invented magnetic angle changing (MAC) device to these experiments has allowed the complete scattering geometry to be accessed for the first time, and experimental methods adopted in these new experiments are discussed here. Data are presented for excitation of the 4 1 P 1 state of calcium by electron impact at scattering angles from near 0 • to beyond 180 • , with incident energies of 45 eV and 55 eV. The results are compared to the DWBA theory of Stauffer and colleagues, with generally excellent agreement.

Experimental results are reported for the (e, 2e) differential ionization cross-section from the 3σg and 1πu valence molecular orbitals of molecular nitrogen N2 at incident electron energies between 25.6 and 76.7 eV. The measurements have been conducted in a coplanar symmetric geometry in an energy regime where ionization is sensitive to contributions from shape resonances and autoionizing doubly excited states. The results suggest that these additional channels may contribute to the measured cross-section. The measurements also display trends qualitatively similar to previous results at higher incident electron energies using the same geometry.