A study for solving the accidental degeneracies in the rotational energy and the frequency formula of C3v symmetric top molecules

The quantized rotational energy and frequency for polyatomic molecules have been studied through the Hamiltonian matrix diagonalization and perturbation theory. Some rotational quantum number sets have accidental degeneracies, which means that the denominator of the second-order energy correction goes zero. The direct matrix diagonalization method has been applied to solve these accidental degeneracies. The corrected energy and frequency terms obtained have been applied to the experimental rotational frequency of CH3CCH and (CH3CN)-N-15 molecules.