Site-specific fragmentation following Si:2p core-level photoexcitation of F3SiCH2Si(CH3)3 in the vapor phase

Abstract

Site-specific fragmentation following Si:2p photoexcitation of (trifluorosilyl) (trimethylsilyl)methane [F3SiCH2Si(CH3)3 (FSMSM)] has been studied by means of photoelectron-photoion and photoion–photoion coincidence techniques. The total photoionization efficiency curve of FSMSM has only one broad peak near the Si:2p core-ionization threshold and no evidence is obtained for the occurrence of selective excitation of each of the two Si atoms. From the results of ab initio calculations of FSMSM, it is found that the magnitude of the Coulomb interaction between the valence electrons and the Si:2p core electrons is very similar at the two Si sites. As a result, the difference in the chemical shift of the 2p core level between the two Si sites is very small. However, the evidence for site-specific fragmentation of the molecule following the Si:2p core-level photoexcitation is obtained by analyzing the photoion–photoion coincidence spectra; the relative yields of H+–SiF+ and CH+n–SiF+3 (n=1–3) ion pairs are enhanced around 104.5 eV, and those of CH+3–F3SiCH2Si(CH3)+2, CH+3–SiCH3F+2, CH+3–Si(CH3)2F+, and H+–SiCH+3 are enhanced around 107 eV. These two thresholds are interpreted to correspond to the 2p core-level photoexcitation at the Si atom bonded to three F atoms and that at the Si atom bonded to three CH3 groups. Ionic fragmentation following excitation of these core electrons occurs selectively around the Si atom where the photoexcitation has taken place. The site-specific fragmentation scheme can be explained on the basis of the valence electron density around the excitation site.

Photoionization and ab initio study of trichloromethylsilane

“…11,12 For polyatomic ions, numerous dissociation channels are available. [13][14][15] Isomerization and rearrangement of a nascent fragment cation might also occur upon photoionization. 16 Photoionization mass spectrometry ͑PIMS͒ is an important complementary method to investigate fragmentation processes of molecules upon ionization, 6,[17][18][19][20][21][22][23] besides giving an accurate adiabatic ionization energy of a transient species, this method is widely applied to determine appearance energies ͑AEs͒ of a radical cation via dissociative photoionization.…”

Dissociative Multiple Ionization following Valence, Br(3d), and Si(2p) Inner Shell Photoexcitation of SiBr4 in the Range of 30−133 eV

“…Energetics, spectroscopy, and dynamics of the core−hole excited states involving core levels of Si(1s), − Si(2s), and Si(2p) − have been investigated by various methods such as X-ray photoabsorption spectroscopy, − the discrete variational (DV) Xα method, multiple-scattering (MS) Xα method, and electron energy loss spectroscopy . All the previous studies of silicon-containing molecules show that the transition of Si(2p) core electron to the first antibonding orbital occurs when the incident photon energy reached about 103 eV, the value being more or less shifted with different ligands.…”

Site-specific fragmentation in condensed (CH3S)2 by sulfur K-edge photoexcitation

“…[13][14][15][16][17][18][19][20][21][22][23][24] In comparison with gas-phase molecules, the mechanism of the site-specific photochemical reaction at solid surfaces is still open owing to the complexity of the decay dynamics in solid or its surface. The main origins of the complexities of the decay dynamics in solid or its surface are; ͑i͒ effect of the inelastically scattered electrons on the fragmentation, ͑ii͒ screening effect by adjacent atoms on the decay processes, and ͑iii͒ structural factors such as crystal structure of solid and molecular orientation of adsorbates.…”