The rotational spectrum of 15ND. Isotopic-independent Dunham-type analysis of the imidogen radical

none6siThe article was received on 16 Jul 2018, accepted on 14 Sep 2018 and first published on 17 Sep 2018The rotational spectrum of 15ND in its ground electronic X3Σ- state has been observed for the first time. Forty-three hyperfine-structure components belonging to the ground and ν = 1 vibrational states have been recorded with a frequency-modulation millimeter-/submillimeter-wave spectrometer. These new measurements, together with the ones available for the other isotopologues NH, ND, and 15NH, have been simultaneously analysed using the Dunham model to represent the ro-vibrational, fine, and hyperfine energy contributions. The least-squares fit of more than 1500 transitions yielded an extensive set of isotopically independent Ulm parameters plus 13 Born-Oppenheimer Breakdown coefficients Δlm. As an alternative approach, we performed a Dunham analysis in terms of the most abundant isotopologue coefficients Ylm and some isotopically dependent Born-Oppenheimer Breakdown constants δlm [R. J. Le Roy, J. Mol. Spectrosc., 1999, 194, 189]. The two fits provide results of equivalent quality. The Born-Oppenheimer equilibrium bond distance for the imidogen radical has been calculated [rBOe = 103.606721(13) pm] and zero-point energies have been derived for all the isotopologues.mixedMelosso, Mattia; Bizzocchi, Luca; Tamassia, Filippo; Degli Esposti, Claudio; Canè, Elisabetta; Dore, LucaMelosso, Mattia; Bizzocchi, Luca; Tamassia, Filippo; Degli Esposti, Claudio; Canè, Elisabetta; Dore, Luc