Vibrational—Rotational Spectrum of Difluoroborane and Difluoroborane-<i>d</i>

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.