The Molecular Structure and Force Constants of Boron Trifluoride and Boron Trichloride

The interatomic distances and the mean amplitudes of BF3 and BCl3 have been determined, by the sector-microphotometer method of gas electron diffraction, to be: rg(B—F)=1.3156±0.0044 Å, rg(F···F)=2.2733±0.0041 Å, l(B—F)=0.0398±0.0029 Å, and l(F···F)=0.0541±0.0020 Å for BF3 and rg(B—Cl)=1.7421±0.0044 Å, rg(Cl···Cl)=3.0134±0.0060 Å, l(B—Cl)=0.0505±0.0023 Å, and l(Cl···Cl)=0.0700±0.0023 Å for BCl3. The force constants have also been determined from the mean amplitudes. Their values are in good agreement with those obtained by the isotopic shifts and by the Urey-Bradley force field. The complex scattering factors for B, F, and Cl have been calculated from the Hartree-Fock potential, and it has been shown that the background intensity and the mean amplitudes of BF3 and BCl3 are much better accounted for by these scattering factors than by those calculated from the Thomas-Fermi potential.