Dynamics and infrared spectroscopy of the protonated water dimer.

We discuss the spectral signatures in terms of the underlying couplings and dynamics of the different degrees of freedom and compare our results to recent, accurate experiments on this system. For the first time the doublet signal at about 1000 cm � 1 is fully reproduced, analyzed, and assigned. The doublet is found to arise from the coupling between the proton-transfer mode and low-frequency, large-amplitude displacements of both water molecules. Predictions are also made for the lowest-frequency part of the spectrum, which has not yet experimentally been accessed. Several important features of the system are analyzed for the first time, namely

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