Nuclear Quadrupole Spectra of Boron Trichloride and Tribromide

概要

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The pure quadrupole resonance spectra were observed on Cl^<35> and Cl^<37> in BCl_3 and Br^<79> and B^<31> in BBr_3 at several temperatures. The spectrum of each nucleus consists of characteristic doublet (^ν<I> and ^ν<II>) with the intensity ratio of ca. 3 to 5. The Zeeman study with a single crystal of BBr_3 was also carried out at liquid nitrogen temperature (77°K), to determine the asymmetry parameter η. The results are as follows: [table] The ionic character and the double bond character were estimated to be i = 0.42 and f = 0.11, respectively for the B-Br bond from the above results. In BCl_3, f = 0.06 was obtained by assuming i = 0.50. The double bond characters of these compounds are fairly smaller than usually assumed. The doublet separation cannot be explained by direct nuclear dipole-dipole interaction. A reasonable explanation was made by taking into account the effect of the intramolecular vibration: the isotopes of boron B^<10> and B^<11> provide different mean square amplitudes to the bending vibrations of BX_3, which in turn produce a difference of q for B^<10>X_3 and B^<11>X_3 molecules. The effect was calculated by use of the normal frequencies of BCl_3 and BBr_3. A fair agreement was obtained between the observed separation of the doublet and hte calculated one. The observed intensity is also compatible with the assumption.
社団法人日本物理学会の論文
1958-08-05