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 HCO·(HO) and NO·(HO). 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.