The ground vibrational and electronic (vibronic) state exhibits a simple rigid rotor-type rotational spectrum. However, each rotational state exhibits fine and hyperfine structure, due to the spin-orbit and electron-nucleus interactions, respectively.
The ground vibrational and electronic states exhibit a simple rigid rotor-like rotational spectrum, but each rotational state shows fine and hyperfine structure due to spin-orbit and electron-nucleus interactions, respectively.