HCl accommodation, dissociation, and propensity for the surface of water

A new reactive and polarizable molecular model was developed to describe HCl dissociation in liquid water and used to investigate HCl behavior at the air-water interface. It was found that the mechanism of HCl accommodation at the air-water interface began with its hydrogen pointing toward the water as it approached from the air. This was followed by dissociation into a contact ion pair once solvated at the air-water interface with the hydronium oriented more toward the air than the chloride on average. In comparison with NaCl, HCl showed some similar behavior in that its contact ion pair was stabilized at the air-water interface in comparison with the bulk. However, dissociated HCl had a greater propensity for the air-water interface than NaCl due to the fact that the hydronium ion was more surface active than sodium.