Spectroscopy of AlO: Combined analysis of the A2Πi → X2Σ+ and B2Σ+ → X2Σ+ transitions

Abstract A combined analysis of the A 2 Π i  →  X 2 Σ + and B 2 Σ +  →  X 2 Σ + band systems of AlO, involving 21,500 line assignments, has been performed. The analysis indicates that the previously reported γ values of the B 2 Σ + state are questionable. The present analysis shows that γ ( B 2 Σ + ) ≈ 0.014 cm −1 , essentially independent of the vibrational level. The positive sign is consistent with second order interaction with the higher-lying C 2 Π r and lower-lying A 2 Π i states. It also appears that many of the previously reported γ and γ D values of X 2 Σ + ( v  > 0) are doubtful. In fact, γ ( X 2 Σ + ) is observed to become increasingly negative for v ″ > 1, due to second order interaction with the low-lying A 2 Π i state. The present results are based on models where the hyperfine structure of the 2 Σ + states has been taken into account explicitly. Intensity patterns of the branches of the B 2 Σ +  →  X 2 Σ + system have been shown to be influenced by the case bβ S coupling in the ground state v  = 0,1 levels. This gives rise to intensity differences of around 10 percent in the R 1 / R 2 and P 1 / P 2 doublet components. The synthesized intensity patterns are fully in accord with the F 1 / F 2 assignments of the present work.