We present a study of the Si K-edge absorption spectra of the Si(X)4 (X = Cl, F, CH3) gas-phase molecules. Both the near-edge and the EXAFS (extended x-ray absorption fine structure) 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 has been employed for phase-shift 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. The presence of an important multiple-scattering high-frequency signal in the EXAFS spectra is evidenced and a very good agreement with multiple-scattering calculations has been found. In this way absorption spectra are shown to be a reliable probe to investigate the three-body distribution in these molecular systems.
X-ray Absorption Investigation of Six4 (x = Cl, F, Ch3)
DI CICCO, Andrea;STIZZA, Sergio;
1992-01-01
Abstract
We present a study of the Si K-edge absorption spectra of the Si(X)4 (X = Cl, F, CH3) gas-phase molecules. Both the near-edge and the EXAFS (extended x-ray absorption fine structure) 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 has been employed for phase-shift 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. The presence of an important multiple-scattering high-frequency signal in the EXAFS spectra is evidenced and a very good agreement with multiple-scattering calculations has been found. In this way absorption spectra are shown to be a reliable probe to investigate the three-body distribution in these molecular systems.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
