Microwave Spectrum, Structure, Dipole Moment, and Barrier to Internal Rotation of Phosphorus Trifluoride—Borane

Abstract

The microwave spectrum of several isotopic species of phosphorus trifluoride—borane (F₃PBH₃) has been measured and the following structural parameters determined: d(BH) = 1.207±0.006 Å; d(PF) = 1.538±0.008 Å; d(PB) = 1.836±0.012 Å; ∠HBH=115°04′±1°; ∠FPF=99°50′±1°. The dipole moment was evaluated from Stark splittings as 1.64±0.02 D. The vibrational satellite spectrum associated with the excited ν₁₂(E) and ν₆(A₂) states for F₃P¹¹BH₃ was found to be strongly perturbed and was fitted to the theory for a first‐order Coriolis interaction. The analysis of this perturbation and the measurement of the ν₁₂ fundamental in the infrared spectrum permitted the inactive torsional fundamental ν₆ to be determined as 197±5 cm⁻¹. This leads to a potential barrier to internal rotation of 3240±150 cal/mole. The enthalpy of dissociation for the reaction 2 F₃PBH₃⇆2 PF₃+B₂H₆ (298°) was determined as 10.99 kcal. The experimental results are compared to those found for other related compounds.