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.