Rotational analysis of the A2Π3/2-A′2Δ5/2 bands of LaS and evidence of interaction between the two spin components of the A′2Δ state

► Emission spectroscopy of the A2Π-A′2Δ transition of LaS. ► Rotational analysis of 16 bands with v′ = 5, v″ = 5 of the A2Π3/2-A′2Δ5/2 sub-band. ► Interaction between the A′2Δ5/2 (v) and A′2Δ3/2 (v + 2) levels of the A′2Δ state. ► Improved spectroscopic constants for the two electronic states.