Vibrational Spectra of BBr3 and BI3

Abstract

The preparation and handling of high purity boron tribromide (BBr₃) and boron triiodide (BI₃) are described. The infrared absorption spectra of BBr₃ in the gas, liquid, and CS₂‐solution phases and of BI₃ in the gas, CS₂‐solution, and solid phases at room temperature are presented and analyzed. The observed BI₃ spectrum is consistent with the expected planar configuration. The hitherto unpublished fundamental vibrational frequencies for BI₃ are used along with those for BF₃, BCl₃, and BBr₃ in a uniform force constant calculation based on a modified valence force potential. The fundamental frequencies for these four molecules should prove useful in testing various potential functions and the force constants should be valuable in predicting the vibrational fundamental frequencies in molecules such as BClI₂ and BBr₂I. The bond stretching force constant for the boron‐iodine bond is 1.95×10⁵ dynes/cm. The boron‐iodine distance in BI₃ is discussed and a tentative value of 2.10 A is proposed.