The vibrational spectrum of the water trimer: Comparison between anharmonic ab initio calculations and neon matrix infrared data between 11,000 and 90 cm−1

► Tunneling effects accounting for the reversible temperature dependence of the infrared spectrum. ► Evidence for intermolecular couplings from degeneracy lifting of the OH-bonded stretching modes. ► Comparison between observed and calculated anharmonicity leading to an accurate assignment of two- and three-quanta vibrational transitions.