Generalized Oscillator Strength Profiles for Inner Shell Excitation of CO2 Derived from Variable Angle Electron Energy Loss Spectroscopy

T. Tyliszczak, I.G. Eustatiu, A.P. Hitchcock,

Dept. of Chemistry. McMaster University, Hamilton, ON, L8S 4M1, Canada

and C.C. Turci, A.B. Rocha and C.E. Bielschowsky

Instituto de Química, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ 21910, Brazil

(Received 12 Aug 2000; accepted 10 Oct 2000)

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 - 62o). 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 => nssg (536.5, 539 eV) and npsu Rydberg states (~539 eV) but not for p 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.

@ 2001Elsevier Science B.V. All rights reserved.