Rotational Analysis of the C²Π → X²Σ⁺ Electronic Transition of LaO

A rotational analysis of the 0–0 band of the LaO C 2 Π r → X 2 Σ + transition near 4400 Å has revised the previously reported analysis. It is demonstrated that the C 2 Π state is also the upper state of previously analyzed bands near 6500 Å. It is shown that the X state of LaO is 2 Σ + and that an interaction between the unpaired electron and the La nuclear spin causes a doubling (0.51 cm −1 ) of each rotational level. This splitting appears to show a slight rotational dependence and a negligible vibrational dependence. The coupling of the X 2 Σ + state is nearly pure case b βS . The C 2 Π r state exhibits a large Λ doubling. The 0–0 subband origins are at 22 839.61 for the C 2 Π 3/2 → X 2 Σ + and 22 618.87 cm −1 for the C 2 Π 1/2 → X 2 Σ + . Rotational spectroscopic constants are reported.