Rotational energies of Hund's case (c) 3Π states in diatomic molecules: The a3Π state of InH and InD

The general theory of the rotational energies and fine structure of a case (c) and intermediate case (c)-case (e) ³Π state is investigated. The theoretical results are then applied to the a³Π state of InH and InD. Certain anomalies in the Λ-doubling of the ³Π₁ substate indicate that the ³Σ⁺ state derivable from the lowest level of the separate atoms is stable with a potential minimum below that of the a³Π state. The stability of this ³Σ⁺ state also yields a reasonable explanation for the predissociation observed for all the a³Π substates. The good agreement between observed and theoretical results regarding the centrifugal distortion in the multiplet splitting shows that the a³Π state is close to coupling case (a) in its lowest vibrational level. However, an increasing case (c) transition occurs with increasing vibrational quantum number.