Line strengths of diatomics. The b 1Σ+ → X 3Σ− transition of the NH and ND radicals

The rotational line strengths of the O- and S-branches in the spin-forbidden emission ND are reported and a comparison is made with the same quantities for NH that have been redetermined. This has led to the following conclusions: (i) In both radicals, a line by line agreement with Watsonʹs theoretical expressions has been observed. This is despite the neglect in the model of spin-spin coupling with respect to spin-orbit. (ii) The isotopic effect is found to be negligible in the spectral range examined, with a single value for the transition moment ration, μ0/μ1 = −0.29, for both radicals. This value agrees with a recent ab inition calculations on NH, supporting the underlying assumptions.