X-ray absorption spectra of SiF4 and Si(CH3)4 in the Si K-shell excitation region

X-ray photo-absorption (XA) spectra of SiF4 and Si(CH3)4 have been measured in the Si K-shell transition region using monochromatized undulator radiation and theoretical calculations have been performed within the framework of density functional theory. For SiF4 main peak structures of the XA spectrum have been reproduced well with the calculation. Further we theoretically simulated a small peak of Si:1s→6a1 excitation, by sampling distorted geometries using classical trajectory calculations at the ground state, which is a forbidden transition under the dipole selection rule. For Si(CH3)4 only one peak was observed and reproduced well with the calculation, which was ascribed to the characteristic of broad Rydberg orbitals coupled with valence orbitals.