Electron momentum spectroscopy studies on atom and molecules using monochromated electrons

A recently developed electron monochromator has been used in noncoplanar symmetric electron momentum spectroscopy studies on atomic argon and molecular cubane. This (e,2e) monochromator typically produces beam currents of 30μA, at better than 98% focus to the inner Faraday cup, into the interaction region. Contemporary work has concentrated on incident electron beam energies in the range 500-1800 eV. At these energies the overall coincident energy resolution is usually in the range 0.50-0:62 eV (FWHM). Binding energy spectra, at different values of recoil momenta, for both argon and cubane, highlight the performance of the spectrometer and will be presented. In addition, selected momentum distributions (MDs) for the respective valence orbitals in both argon and cubane will also be given. These MDs are compared against theory calculations made within either a distorted wave impulse approximation (argon) or plane wave impulse approximation (cubane) reaction mechanism framework. For the argon calculations Hartree-Fock orbitals were employed, while for cubane an extensive range of density functional theory basis sets were used. Some of the ramifications of the present results will be discussed.