A method of calculating rotationai constants for diatomic molecule or radicai by using its vibrational constants

A method of calculating rotational constants for diatomic molecule or radical is given by using RKR equation involved only with its rotational constants and morse function approximation based on abinitio calculation or experiment. As an example, we calculate the rotational constants for the ground state and excited states of CN radical, the results obtained are consistent with the experimental results very well.