MICROWAVE SPECTRUM VIBRATION-ROTATION INTERACTION MOLECULAR STRUCTURE AND DIPOLE MOMENT OF 1-METHYLPENTABORANE (9)

The microwave spectra of a number of isotopic species of 1-methylpentaborane (9) have been analyzed. All spectra are consistent with a model having free internal rotation and vibration-internal-rotation interactions. Lack of barrier perturbations leads to an upper limit of 1 cm -1 for the 12-fold barrier. The theory for the vibration-intemal- rotation interaction is extended to low-barrier molecules having an N-fold. barrier. The boron framework was determined to be identical with that in pentaborane (9). The dipole moment is 1.93±0.05 D.