2D-IR correlation analysis of thin film water adsorbed on α-Al2O3 (0 0 0 1)

The spectral characteristics of adsorbed thin film water on α-Al2O3 (0 0 0 1) were investigated using infrared spectroscopy. Extinction spectra were collected as the amount of water vapor in the sample chamber was changed as a function of relative humidity (20–100%). A moving window correlation analysis elucidated areas of large spectral changes and further 2D-IR correlation analysis provided insight into the changing hydrogen bonding environments of adsorbed thin film water between 25% and 40% RH. At 30% RH or 2–3 layers of adsorbed water, a supermolecular connected water layer exists above which additional water molecules cannot penetrate and are forced to form higher energy hydrogen bonding environments. A BET analysis also supports an adsorbed thin film of 2–3 water layers to have similar properties different than submonolayer or multilayer water coverages.