An infrared spectroscopic study of water thin films on NaCl (100)

Using infrared spectroscopy, we were able to determine that water adsorbs onto the surface of NaCl (100) in a liquid-like thin film over the temperature range of -27 degrees C to 40 degrees C. Photometric methods allow coverages to be monitored from near 0.1 monolayer to over three monolayers. The shifting band center of the OH stretching vibration absorption indicates changing hydrogen-bonding environments with coverage. Below a monolayer the band center is blue-shifted relative to liquid water absorption, suggesting some sort of unique hydrogen bonding arrangement. In the region between one and two monolayers, the coverage and change of band center with relative humidity appears discontinuous. Coverages near two monolayers produce spectra essentially indistinguishable from that of a saturated salt solution, suggesting a liquid-like hydrogen-bonded network, even at temperatures as low as -27 degrees C. A model for thin film water growth on NaCl (100) is proposed. (C) 1999 Elsevier Science B.V. All rights reserved.