Core level photoionization mass spectroscopy of the fluoromethylsilanes, Si(CH 3) xF 4- x ( x = 0–4), around the Si 2p ionization edges

Abstract

Total ion yield spectra, total electron yield spectra, photoionized mass spectra and mass resolved partial photoion yield spectra of the five fluoromethylsilane compounds, Si(CH 3) x F 4- x ( x = 0–4), measured around the Si 2p core ionization edges using monoc synchrotron radiation are reported. Photoionized mass spectra of the five compounds were also measured around the Si 2s and F 1s ionization edges. For each of the fluoromethylsilane compounds, total ion yield and total electron yield spectra are very similar to each other and to the corresponding photoabsorption spectra with the exception of the decreased intensities of the discrete resonances. The photoion mass spectra show that almost all possible molecular fragments are generated by excitation and ionization of the Si 2p, Si 2s and F 1s core electrons. Branching ratios of the photoion mass spectra peak areas indicate that the methyl groups are much more labile than the fluorine atoms at all photon energies, both below and above the core ionization edges, in the mixed fluoromethylsilane compounds. Relative areas of the methyl peaks in the photoion mass spectra are enhanced at the discrete resonances below the ionization threshold with more pronounced enhancements above the ionization threshold. An explanation for the greater lability of the methyl ligands is proposed based on the effect of the electron withdrawing and donating properties of the fluorine atoms and methyl groups which also affect the relative Auger transition rates and core hole lifetimes. Partial ion yields of the SiF + and SiMe + fragment ions also exhibit some specific enhancements at Si 2p→σ* resonances below the ionization edge.