ESCA: A theoretical intensity model based on the plane-wave approximation

In this paper, we first of all present a rather simple and convenient theoretical equation, based upon the plane-wave approximation, for the differential cross-section for photoionization of a polyatomic molecule. Next, we derive an intensity model specific for X-ray photoelectron spectra of a general molecule containing first-row atoms. Applications of the model to CH₄, H₂O, N₂, CO, CF₄, and CH₃OH give very satisfactory results compared with experimental ESCA relative intensities. Similarities and differences between our theoretical model and Gelius' semiempirical model are pointed out and discussed.