Inner-shell electron energy loss spectroscopy and generalized oscillator strengths at high momentum transfer.

摘要

Detailed information about the energies of the electronically excited and ionized states of atoms and molecules is of central importance to the understanding of the interaction of energetic radiation with matter. Such data permits a more complete understanding of various processes taking place in physics, chemistry or biology, with important areas of application including electron and X-ray microscopy, space physics and chemistry or any other area where energetic radiation is used.; This work documents the improvements and performance of a variable scattering angle energy loss spectrometer used to investigate inner-shell electronic spectroscopy of gases and to map generalized oscillator strengths. Wide ranges of impact energy and scattering angle are used to study both electric dipole and non-dipole transitions. New spectroscopic studies include: (i) the observation of the non-dipole “B-state” in SF₆ S 2 p edge at very high scattering angle (62°) and at 1550 eV impact energy, where it dominates the spectrum; (ii) the first experimental observation of the C 1s → σ_g* transition in CO₂. Generalized Oscillator Strength (GOS) profiles were mapped systematically for a collection of molecules: in SF₆, the GOS for S 2p and S 2s were extended up to very high momentum transfer, while the GOS for F 1s was mapped here for the first time. GOS curves were also obtained for all edges in CO ₂, COS and CS₂, some of them revealing their shapes for the first time. Where available, the results were compared to theoretical calculations. This work greatly extends previous reported studies of GOS for inner-shell excitation.