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--HO 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.