Vibrating hydroxide in hydrophobic solution: The ion to keep an eye on

Knowledge of hydroxide ion’s spectral signature is an essential ingredient for finding it at the water surface. In solutions, the intense hydrogen-bonded resonance of water often hinders unambiguous characterization of the OH− stretching frequency and linewidth. These parameters are likely to be modified at the hydrophobic water–vapor interface. This communication reports the first experimental observation of hydroxide ion that is free from interaction with bulk water. OH− is isolated in a hydrophobic environment and exhibits a sharp resonance at 3634 cm−1, as confirmed by isotopic substitution. The feature is red shifted from that of dangling OH bonds by 29 cm−1.