The 3ν3 + 2ν2 band of O3 appearing in the 4325 cm-1 region has been observed for the first time using the FTS of Reims (resolution. 0.004 cm-1) and a very large pl (pressure × pathlength) product: 50 Torr × 36 m. This band has been analyzed using the Watson-type Hamiltonian, including the Coriolis resonance with the ν + 2ν2 + 2ν3 band. Transitions have been observed up to J = 35 and Ka = 11, the maximum absorption being 10% for the most intense line (5 × 10-25 cm-1/molecule·cm-2). A few levels have been found to be slightly perturbed. The perturbing levels have been identified: they belong to the 400 vibrational level, the 4ν2 being much too weak to be observed without this perturbation. Furthermore, 64 line intensities have been used and led to the transformed transition moment. Fits for both energy levels and intensities are satisfactory. Finally, a complete list of line positions, intensities, and lower state energies has been generated for the 3ν3 + 2ν2 band of 16O3. © 1993 Academic Press, Inc.