X-ray absorption investigation of SiX4(X=Cl,F,CH3)

The authors present a study of the Si K-edge absorption spectra of the Si(X) 4 (X=Cl,F,CH 3 ) gas-phase molecules. Both the near-edge and the EXAFS (extended X-ray absorption fine structures) regions are analysed. These simple molecules have been chosen to test multiple-scattering theory in the case of open structures with no second neighbours. Hedin-Lundqvist complex self-energy (1969) has been employed for phaseshift generation. Data analysis demonstrates the presence of strong multiple-scattering effects in the near-edge region. Near-edge structures are interpreted in terms of two-body and three-body contributions. A fitting procedure taking account of the presence of a KL double-electron excitation has been adopted to investigate the EXAFS region. Determination of distances using such an ab initio procedure is shown to be in agreement with diffraction data.