Vibronic and Rotational Energy Levels of a Linear Triatomic Molecule in a 3Π Electronic State

Expressions are presented for the vibronic and rotational energy levels of a linear triatomic molecule in a 3Π electronic state which take into account spin‐orbit and vibronic (Renner) interactions. The results are valid when both interactions are small compared to the frequency of the bending vibration. It is shown that the vibronic energy levels can be divided into two sets, such that the energies of one set are like those of the vibronic states of a 1Π electronic state, whereas the energies of the other set are like those of the vibronic states of a 2Π electronic state. Some similarities and differences between the expressions for the rotational energy levels presented here and the corresponding expressions for diatomic molecules are discussed.