Résumé : The jet-cooled spectrum (Trot = 12K) of the H2O–CO2 van der Waals complex has been recorded in the 1.4 μm region by cavity ring-down spectroscopy. Two b-type vibrational bands have been observed and analysed. The rotational assignment has been achieved using a different asymmetric rotor Hamiltonian for each nuclear spin species, accounting for the internal rotation of the H2O and CO2 units. The band at 7247 cm-1 is assigned to (101) in terms of the (v1v2v3) vibrational quantum number of the H2O monomer. The band at 7238 cm-1 is assigned to (200) + an intermolecular mode (v12) excited in the complex. Vibration-rotation constants are provided for the excited states. The symmetry of the wavefunction, the effect of vibrational excitation on the tunnelling dynamics and the vibrational assignment are discussed.