ABSTRACT
The pure rotational spectrum driven by the small distortion dipole moment perpendicular to the symmetry axis has been investigated between 8 and 18 GHz for CH3CF3 in the ground vibrational state using a pulsed Fourier transform waveguide spectrometer. This molecule has been selected as a prototype for the case of a symmetric top with small ( approximately 500 kHz) torsional energy splittings in the ground torsional state (nu6 = 0). In this state, six (k +/- 3 <-- k) Q-branch series have been measured for lower state K = |k| between 3 and 8 with 27 = J = 75. For (nu6 = 1), three series with lower state K between 5 and 7 with 49 = J = 66 have been observed. In two of these series, the torsional fine structure extending over approximately 6.8 MHz has been fully resolved. The (A1 - A2) splitting has been measured in the (nu6 = 0) series (K = 6 <-- 3) for 37 = J = 74. The global data set of 443 frequencies included avoided-crossing molecular-beam splittings of Meerts and Ozier (1991. Chem. Phys. 152, 241-259) and mm-wave R-branch measurements of Bocquet et al. (1994. J. Mol. Spectrosc. 165, 494-499). In a weighted least-squares analysis, a good fit was obtained by varying 18 parameters in a Hamiltonian that represented both the torsional effects and the sextic splittings. Effective values have been determined for both rotational constants, eight torsional parameters including the barrier height, six diagonal centrifugal distortion constants, and two centrifugal distortion constants (epsilon and epsilonJ) that characterize the (Deltak = +/-3) matrix elements. The difficulties are discussed that arise in defining a unique model for the torsional terms in the Hamiltonian when a high barrier symmetric top is investigated by distortion moment spectroscopy. The redundancies are investigated that exist in the quartic and sextic Hamiltonian for a near-spherical top such as CH3CF3. Copyright 1998 Academic Press.
ABSTRACT
Rotational spectra of the unstable molecules FBO, ClBO, and FBS have been measured in the 8-26 GHz frequency range using a pulsed jet cavity Fourier transform microwave spectrometer. The samples were prepared by passing electric discharges through mixtures of O2/BF3, O2/BCl3, or OCS/BF3, respectively, entrained in Ne. Hyperfine structures in the observed transitions have been resolved and analyzed in terms of nuclear quadrupole, spin-rotation, and spin-spin interactions. The quadrupole and spin-rotation coupling constants have been used to show that the electronic environment surrounding the boron nucleus of all three species is very similar. The spin-rotation constants have been used to determine, for the first time, experimental average shieldings of the Cl, F, and B nuclei of these molecules. Ab initio values for the nuclear shielding parameters have been calculated for comparison. Copyright 1998 Academic Press.
ABSTRACT
The pure rotational spectrum of 24Mg14N12C, between 11.9 and 23.9 GHz, has been measured using a pulsed jet Fourier transform microwave spectrometer. The hyperfine structure due to the 14N nucleus has been measured, and the nuclear quadrupole coupling, Fermi contact, and dipole-dipole interaction constants have been determined. The ionic character of the metal-isocyanide bond has been investigated through the nuclear quadrupole and magnetic hyperfine parameters. Copyright 1998 Academic Press.