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Using infrared spectroscopy, we were able to determine that water, under ambient conditions, adsorbs onto the surface of NaCl(100) into a liquidlike thin film. Photometric methods allowed coverages to be monitored from near ϑ = 0.1 (0.1 monolayer) to ϑ = 3. The shifting band center of the −OH stretching region suggests changing hydrogen-bonding environments with coverage. In the submonolayer region, water−surface bonds are favored over water−water hydrogen bonds. Thin film coverages near ϑ = 2 produce spectra essentially indistinguishable from that of a saturated salt solution suggesting a liquidlike hydrogen-bonded network. This thin film can be reversibly removed from the NaCl(100) surface. However, at coverages near ϑ = 3, dissolution begins and the salt surface becomes visibly damaged. Isotherms measured at 12 and 24 °C allowed the determination of the isosteric heat of adsorption. This heat of adsorption for coverages near ϑ = 2 is close to that of the heat of condensation of liquid water, again suggesting that the thin film is liquidlike. A model for thin film water growth on NaCl(100) under ambient and cryogenic conditions is proposed.
Peters et al. (Mon,) studied this question.