MARVEL analysis of the measured high-resolution spectra of [formula omitted]NH.

• Measured Active Rotational-Vibrational Energy Levels technique applied to transitions involving 4 electronic states of NH. • 3002 transitions identified from 18 sources. • 1058 rovibronic energy levels determined. Rovibronic energy levels are determined for four low-lying electronic states (X 3 Σ - , A 3Π, a 1 Δ , and c 1 Π) of the imidogen free radical ( 14 NH) using the M arvel (Measured Active Rotational-Vibrational Energy Levels) technique. Compilation of transitions from both laboratory measurements and solar spectra, found in 18 publications, yields a dataset of 3002 rovibronic transitions forming elements of a measured spectroscopic network (SN). At the end of the MARVEL procedure, the majority of the transitions form a single, self-consistent SN component of 2954 rovibronic transitions and 1058 energy levels, 542, 403, and 58 for the X 3 Σ - , A 3Π, and c 1 Π electronic states, respectively. The a 1 Δ electronic state is characterized by 55 Λ -doublet levels, counting each level only once. Electronic structure computations show that unusually the CCSD(T) method does not accurately predict the a 1 Δ excitation energy even at the complete basis set limit. [ABSTRACT FROM AUTHOR]