Microwave spectrum and structure of difluoromethylborane, CH3BF2
Abstract
Microwave spectra of CH311BF2, CH310BF2 and 13CH311BF2 in the ground torsional state are reported. Moments of inertia derived from the analysis of these spectra together with published data for CD3BF2 have been used to determine the following structure: C—H = 1.102 ± 0.007, C—B = 1.564 ± 0.005, B—F = 1.315 ± 0.005 Å HCB = 110.4 ± 0.5°, FBF = 116.8 ± 0.5°. The structure of the BF2 group in CH3BF2 and other BF2 compounds is shown to be relatively invariant in comparison to that of the isoelectronic NO2 group. Nuclear quadrupole coupling constants at boron are discussed in terms of the structure. The range of transitions studied for the species CH311BF2 and CH310BF2 has enabled a centrifugal distortion analysis to be carried out for the ground torsional state using Watson's reduced Hamiltonian. This has revealed an anomaly for high J, Q-branch transitions which are not satisfactorily fitted by the present treatment. Stark effect measurements give a ground-state dipole moment of µ= 1.668 ± 0.003 D.