Wavefunction quantization of the proton motion in a H5O2+ dimer solvated in liquid water

The infrared spectroscopy of the transient H5O2+ species in liquid water is studied. The potential energy surface of the system is modeled by a two-state Empirical Valence Bond (EVB) model. The quantization of the central proton of the dimer H5O2+ is described by a three-dimensional time-dependent gaussian wavefunction within an adiabatic molecular dynamics simulation, or by using an effective parameterization of the EVE model, using a preliminary path-integral calculation. It is shown that the H5O2+ complex in solution displays a strong absorption between 1000 and 2000 cm(-1). We demonstrate that the contribution of the asymmetric O-H+ stretch cannot be unambiguously assigned, due to its close coupling to the other modes of the dimer. The oxygen-oxygen stretching mode of the dimer strongly modulates the infrared spectrum of the central proton while the effect of the solvent is mainly to induce an asymmetry of the central O-H-O+ bond of H5O2+ leading, partly, to absorption at higher frequencies. (C) 2000 Elsevier Science B.V. All rights reserved.