Vibrational effects on electric and magnetic susceptibilities: applicationto the properties of the water molecule

We present perturbation theory expressions for the pure vibrational contrib utions to the hypermagnetizability. These expressions are complete to secon d order in perturbation theory and include contributions from third derivat ives of the properties and the quartic force constants. We calculate zero-p oint vibrational and pure vibrational effects on the polarizability, magnet izability and hypermagnetizability of the water molecule, and discuss the e ffects of nuclear motion on the Cotton-Mouton constant of water in the gas phase. This is the first investigation of vibrational effects on the hyperm agnetizability of a polyatomic molecule.