Quartet–doublet interactions observed in the emission spectrum of the NO molecule

Emission bands, B 2Π–X 2Π (β-bands), of the NO molecule analyzed fifty years ago by Jenkins, Barton, and Mulliken are revisited. A large 4Σ−∼2Π interaction (H=5.1 cm−1), predictable by recent ’’anticrossing’’ and ’’electron-impact’’ experiments is detected. Additional smaller perturbations are studied. The aim to locate exactly the quartet states with respect to the doublet states is not fully achieved, but the energies of v=0 and 1 of the b 4Σ− state are determined to ±10 cm−1, and several rotational levels are located to ±0.1 cm−1. The sign of the Λ-doubling in the ground state is established.