Hyperfine structure in the rotational spectrum of GaF: A comparison of experimental and calculated spin-rotation and electric field gradient tensors

The high-resolution pure rotational spectrum of Gal; has been measured usin g a Balle-Flygare-type Fourier transform spectrometer. improved nuclear qua drupolar coupling constants and rotational constants have been obtained alo ng with the first reported fluorine spin-rotation constant for gallium fluo ride, C-I ((GaF)-Ga-69-F-19, upsilon = 0) = +32.0(21) kHz. Accurate spin-ro tation tensors from microwave or molecular beam spectroscopy are particular ly important to NMR spectroscopists and theoreticians because these data pr ovide information about anisotropic nuclear magnetic shielding in the absen ce of intermolecular effects. For quadrupolar nuclei such as gallium, the q uadrupolar interaction is sufficiently large that it is very difficult to c haracterize shielding tensors directly via NMR spectroscopy. The experiment ally determined nuclear quadrupolar coupling constants and spin-rotation co nstants for GaF are compared with the results of a series of high-level nb initio calculations carried out at various levels of theory with a range of basis sets. Further calculations on BF and AlF, supplemented with availabl e experimental data for InF and TlF, allow for the investigation of trends in nuclear magnetic shielding, spin-rotation, and electric field gradient t ensors in the group-13 fluorides. Calculations at the MP2/6-311++G** and MP 2/6-311G(2df, 2pd) levels provide the most consistently satisfactory result s in comparison with the experimental data. (C) 2000 Academic Press.