The microwave spectra of CO in the electronically excited states (a 3Πr and a′ 3Σ+)

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Abstract
The rotational transitions of CO in the electronically excited states (a 3Πr and a’ 3Σ+) are observed in the millimeter and submillimeter wave regions. The vibrational satellites are detected up to v=6 for the a 3Πr state and up to v=2 for the a’ 3Σ+ state. The observed spectra are found to be perturbed by the interaction between the a 3Πr and a’ 3Σ+ states, and they are not fitted to conventional formulations for the 3Πr and 3Σ+ states within the experimental uncertainties. A simultaneous deperturbation analysis for the a 3Πr (v=0–7) states and the a’ 3Σ+(v=0–3) states is carried out by using the observed transition frequencies and the reported data of the Λ‐type doubling rf transitions in the a 3Πr state. The detailed molecular constants are obtained for the a 3Πr and a’ 3Σ+ states. These constants show smooth change on the vibrational quantum number. This indicates that they are almost free from the interaction between the a 3Πr and a’ 3Σ+ states.