Detection of perturbation-allowed ΔJ=2 transitions in the millimetre-wave spectrum of 81BrNO

The strong quadrupole resonance between the 120, 12 and 111, 10 ground state rotational levels of 81BrNO has been reinvestigated. A pair of forbidden ΔJ=2 and near-forbidden ΔJ=0 transitions could be detected in the 3.3 mm wavelength region. The analysis of the hyperfine structure of these new lines, due to the coupling of both bromine and nitrogen nuclear spins, allowed us to make an evaluation of the off-diagonal element for the symmetrized spin–rotation tensor of the bromine nucleus. Improved values of the nitrogen quadrupole coupling constants were obtained, from which the principal elements of the corresponding tensor were calculated.