Vibrational—Rotational Spectrum of Difluoroborane and Difluoroborane-d

Abstract

Four HBF₂ and two DBF₂ fundamentals have been resolved into their fine structure under medium dispersion. The three A₁ modes, v₁, v₂, and v₃ are characterized by a series of evenly spaced lines having the general appearance of a ⊥ band of a symmetric‐top molecule. The B₂ modes, v₆, have a strong Q branch in addition to a well‐defined subband system and have the appearance of Type‐C bands near the prolate limit. Using a symmetric‐top approximation, an analysis of the spectra provided six independent measurements for the smallest moment of inertia from which the average apex angle F–B–F was calculated to be 117.4±2° assuming the BH(BD) bond distance to be 1.20 Å. In HBF₂, interband agreement of the rotational constant A, associated with the smallest moment of inertia, was quite good. It was possible to assign K values to the individual lines and to determine the position of the band centers for the resolvable fundamentals v₁, v₂, v₃, and v₆.