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

Abstract

Ionic fragmentation caused by Si:1s photoexcitation of 1-trifluorosilyl-2-trimethylsilylethane [F 3SiCH 2CH 2Si(CH 3) 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(CH 3) 4 and SiF 4, 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 CH 3 groups suppressed the production of CH 3 + and SiCH 3 +. 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 SiF 3 +. 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.