HYPERFINE CONSTANTS AND NUCLEAR SHIELDINGS FROM THE MICROWAVE-SPECTRAOF FBO, CIBO, AND FBS

Rotational spectra of the unstable molecules FBO, CIBO, and FBS have b een measured in the 8-26 GHz frequency range using a pulsed jet cavity Fourier transform microwave spectrometer. The samples were prepared b y passing electric discharges through mixtures of O-2/BF3, O-2/BCl3, o r OCS/BF3, respectively, entrained in Ne. Hyperfine structures in the observed transitions have been resolved and analyzed in terms of nucle ar quadrupole, spin-rotation, and spin-spin interactions. The quadrupo le and spin-rotation coupling constants have been used to show that th e electronic environment surrounding the boron nucleus of all three sp ecies is very similar. The spin-rotation constants have been used to d etermine, for the first time, experimental average shieldings of the C l, F, and B nuclei of these molecules. Ab initio Values for the nuclea r shielding parameters have been calculated for comparison. (C) 1998 A cademic Press.