Generalized oscillator strength profiles for inner shell excitation of CO2 derived from variable angle electron energy loss spectroscopy

Abstract

GOS profiles for C 1s and O 1s excitation of CO2 have been derived from inner shell electron energy loss spectra of CO2 measured over a wide range of scattering angles (4–62°). The experimental profiles are compared to computed GOS profiles calculated within the first Born approximation, using ab-initio configuration interaction wave functions for the C 1s transitions and ab-initio generalized multi structural wave functions for the O 1s transitions. The theoretical and experimental results are in generally good agreement indicating that the first Born approximation holds to a surprisingly large momentum transfer for the core excitations studied. The computations predict there should be oscillations in the GOS for O 1s→nsσg (536.5, 539 eV) and npσu Rydberg states (∼539 eV) but not for π symmetry states. Measurements with a newly installed parallel detector provide experimental support for the existence of oscillations in the GOS profile for the O 1s excitation of CO2 at 539 eV. These oscillations may arise from interference between core excitations localized on the left or right oxygen atom of CO2.