Comment on ‘Behaviour of hydroxide at the water/vapor interface’ [Chem. Phys. Lett. 474 (2009) 241]

These authors claim the lack of appreciable surface enhancement of hydroxide ion at the water/vapour interface, which cannot be sustained. The duration of their liquid microjet experiments at pH 8 is too short to establish equilibrium at the surface. Their measurements at high hydroxide ion concentrations show a weak affinity of hydroxide ions for the interface; extrapolation to low concentrations would not reveal strongly adsorbed hydroxide ions if these were beneath the surface layers probed by the photoelectron spectroscopy. Confusion on this topic arises from invalid inferences about the interface at near neutral pH from observations at high hydroxide concentrations.