Two-Dimensional Adiabatic Model for Calculating Progressions Resulting from Stretch-Rock Coupling in Vibrational Spectra of Anion-Water Complexes.

Several anion-water dimers feature a distinct progression in the OH stretch region of their vibrational spectra. This progression arises from strong anharmonic couplings between the OH stretch and low-frequency intermolecular modes. In this work, we introduce a two-dimensional adiabatic model accounting explicitly for the water and anion rock degrees of freedom and use it to calculate the vibrational spectra of HCO2-·(H2O) and NO3-·(H2O). The spectra calculated by using this model are in excellent agreement with experiment, in terms of both peak spacings and lengths of the progressions, and represent a substantial improvement over earlier models.