Introduction.- General remarks.- Energy level vibrational assignment. Normal modes and Local modes.- Rotational assignment.- Polyads. Energy level vibrational interactions.- A-reduced Watson-type rotational Hamiltonian.- S-reduced Watson-type rotational Hamiltonian.- Perturbation-theory free, Jensen MORBID Hamiltonian.- Jensen’s PES determined by variational calculation of rotation–vibration energies, with MORBID Hamiltonian.- Force field parameters.- Dipole moment.- Line profiles.- References.- O3 data.