IR spectroscopic properties of H(MeOH)(n)(+) clusters in the liquid phase: Evidence for a proton wire

The long-standing problem of understanding the nature of the excess proton in acidified water is simplified by studying the proton in methanol. The 3D network of hydrogen bonds in H-(aq)(+) is reduced to a 1D problem. Infrared spectroscopic characterization of linear chain methanol proton solvates in H(CH3OH)(n)(+) for n=2-8 provides insight into some of the puzzling IR spectral features associated with O-H-O vibrations. These include the virtual disappearance of otherwise strong bands from H-bonded methanol molecules adjacent to symmetrical O-H+-O groups. The data indicate that a chain of up to four O-H center dot center dot center dot O bonds either side of this group can act as an electrical wire to separate positive charge. This suggests a refinement of the Grotthuss proton-hopping mechanism for explaining the anomalously high mobility of H+ in H-bonded media.