Selective observation of boundary water near a solid/water interface by variable-angle polarization specific attenuated total reflection infrared spectroscopy and principal-component analysis

An infrared spectrum of the boundary water near a solid/water interface has been observed, which is distinguished from the bulk water using a novel analytical technique. The technique employs the variable-angle polarization specific (VAPS) attenuated total reflection (ATR) infrared spectrometry and a characteristic of principal component analysis (PCA). To date, near-field optical techniques or artificial polycrystalline water thin-layer formation technique have been used to study the structure of boundary-water molecules below the limitations of spatial resolution. Here, however, we show that the combination technique of VAPS-ATR and PCA analytically overcomes the difficulty of spatial resolution and detection limit, so that we selectively observe the boundary water. The orientation of the boundary-water molecules has been evaluated using the resolved infrared spectra obtained as the PCA loadings. In addition, it was also suggested that there was an intermediate layer between the boundary water layer and bulk water.