Critical examination of prewetting and surface melting on caprolactam

In a previous study, surface melting on the (001) surface of caprolactam (C₆H₁₁ON) was reported to proceed in a series of layering transitions, followed by a prewetting transition. We have reproduced the original results and shown that they can be better explained by the wetting of hydrated caprolactam (with H₂O molecules at bridging sites between the caprolactam dimers) on caprolactam, and that such hydration is most likely caused by H₂O microinclusions in the crystals grown from solution. In agreement with this interpretation, we have also shown that the reported effects are absent on "dry" surfaces.