Microwave Spectrum and Barrier to Internal Rotation in CH3BF2

Abstract

The microwave spectrum of CH₃BF₂ has been observed in the frequency range 12–33 kmc. The identifiable lines are explained in terms of a model consisting of a symmetric top (CH₃) rotating with respect to an asymmetric framework (BF₂) with the top axis coinciding with the (least) principal inertial axis of the molecule. The value of the barrier to internal rotation was determined to be 13.77±0.03 cal. Three moments of inertia were also obtained from the analysis: A = 10586.73 (BF₂ group only), B = 8329.01, C = 4650.52 Mc. These are insufficient to determine the molecular structure, but are consistent with the structure reported from electron diffraction. Stark effect measurements yield a dipole moment of 1.67±0.02 D.