Deciphering spectral signatures of proton delocalization in complexes of hydroxide and hydronium ions with water molecules

One class of system where explorations of larger complexes is particularly instructive involves complexes of ions with water molecules. In these systems the cooperative nature of the hydrogen bond that are formed leads to large changes in the strengths of the ion-water interactions as more water molecules are introduced, and this, in turn, has a large effect on the spectroscopy. This talk will focus on work in our group exploring the most fundamental ion-water complexes, those between water molecules and hydronium or hydroxide ions. This work employs an array of theoretical and computational approaches, ranging from analysis of the couplings of the vibrations at the harmonic level through analysis of the wave functions using diffusion Monte Carlo approaches. The work is motivated by the studies of the vibrational spectra of complexes of hydronium and hydroxide ions with up to five water molecules. Interestingly, as the number of solvating water molecules is increased from one to three, the frequency of the OH bond involved in the ion/water interaction experiences a large blue-shift with very similar spectral contours being observed for the complexes of hydroxide and hydronium ions with water.