Site-specific fragmentation caused by core-level photoexcitation: Comparison between Si:1s and 2p photoexcitations in F3SiCH2CH2Si(CH3)3 vapor

Ionic fragmentation caused by Si:1s photoexcitation of 1-trifluorosilyl-2-trimethylsilylethane [F3SiCH2CH2Si(CH3)3] vapor was studied using monochromatized synchrotron radiation and a reflectron-type mass spectrometer. The total ion-yield spectrum in the Si:1s excitation region was found to be very similar to the superposition of the ion-yield spectra of Si(CH3)4 and SiF4, showing that site-specific excitation occurred in this molecule. When the photon energy was scanned from low to high, the 1s → σ* excitation at the Si atom bonded to three CH3 groups suppressed the production of CH3+ and SiCH3+. The 1s → σ* excitation at the Si atom bonded to three F atoms, on the other hand, enhanced the production of F+ and SiF+ and suppressed the production of SiF3+. These results suggest that Si:1s site-specific excitation causes site-specific fragmentation. The fragmentation caused by Si:1s → σ* photoexcitation was also found to be more violent than that caused by Si:2p → σ* photoexcitation.