Isotopically invariant analysis of vibration-rotation transitions of HBr and its isotopologues

The vibration-rotation transition frequencies of HBr and its isotopologues reported in the literature were simultaneously analyzed in a least-squares fit to determine isotopically invariant molecular parameters Ukl and Born-Oppenheimer breakdown parameters Δkl. A total of 692 lines was fitted to Watson's expression involving 25 adjustable parameters to a weighted unitless standard deviation of σ ≈ 0.91. From new data in the far-infrared region and those of improved precision in the mid-infrared and the near-infrared region, the breakdown parameters for the bromine atom were determined; the parameter Δ10Br for the harmonic frequency improved the fit and Δ01Br for the rotational constant enabled us to obtain the information on the adiabatic correction to the Born-Oppenheimer approximation.