High-energy photoelectron C 1s and O 1s shake-up spectra of CO

K-shell photoionization in CO molecules is studied experimentally and theoretically. High-resolution O 1s and C 1s shake-up spectra were recorded using monochromatized Al K-alpha radiation. The experimental data are compared with the results of Green function calculations employing a new complete fourth-order approximation scheme. The O 1s and C 1s satellite structures are found to differ strikingly already at low shake-up energy. An explanation of this behavior is given in terms of intramolecular charge transfer associated with valence excitations.