Gas-phase generation and structural characterization of [H2, C, O, Si].bul.+ and [H2, C, O, Si] by collisional-activation and neutralization-reionization mass spectrometry and theory: evidence for the distonic ion H2C.bul.-O-Si+ and the biradical CH2OSi

Abstract

Results of laboratory measurements and theoretical investigations are reported which provide evidence for the stability of the distonic ion 'CH,OSi+ and which show that the biradical species 'CH20Si' may be generated by the neutralization of the distonic ion in the gas phase. The measurements were made using collisional-activation and neutralization-reionization mass spectrometry. Ions of the type (H,, C, 0, Si) were generated by electron-impact ionization of Si(OCH3), at 70 eV. Observed collisional-activation (CA) mass spectra of these ions at 8-keV translational energy are most compatible with the connectivity 'CH,OSi+. Neutralization-reionization (NRMS) experiments with this distonic ion suggest an identical connectivity for the corresponding neutral species. The experimental findings are complemented by ab intio MO studies (MP2/6- 3lGS*//MP2/6-31G** +ZPVE) which predict that the heavy-atom backbone of both the distonic ion and the biradical neutral are linear and that they have very similar bond lengths. They also provide useful information on the energetics of the unimolecular decompositions of the distonic ion and the energetics and structures of many of its isomers.