In-plane vibrational frequencies and modified Urey—Bradley force constants of boron trihalides

The validity of various sets of assigned in-plane vibrational frequencies for boron trihalides is discussed by application of the product rule, and by comparison of the signs of symmetry force constants calculated from the observed frequencies with those predicted by using of the hybrid orbital force field. The Urey—Bradley force constants were modified and translated from the general valence force constants so as to be compatible with the information obtained above, and consistent with the empirical data for a series of molecules of this structural type. As a result, it was found that the bond—bond, angle—angle and bond—opposite angle interaction should necessarily be taken into consideration for obtaining the reasonable modification.