Quantum Theory of Atoms in Molecules/Charge–Charge Flux–Dipole Flux interpretation of fundamental vibrational intensity enhancements on H-bond formation of water trimer

The Quantum Theory Atoms in Molecules/Charge–Charge Flux–Dipole Flux model was used to investigate electronic structure variations associated with intensity changes for water trimer vibrations. The total of 440 km mol−1 experimental intensity for the symmetric stretches amounts to an average contribution of 147 km mol−1 per hydrogen bond. The calculated QCISD/cc-pVTZ value is 274 km mol−1. The largest changes on complex formation occur for the charge, charge flux and their interaction. The hydrogen-bonded hydrogen atoms account for 99% of the total intensity of the two strongest symmetric stretches, mostly owing to mechanical vibration factors.