OH stretching vibration changes of water at water-rock interface under high temperatures and pressures: An in-situ study using infrared spectroscopy

In order to investigate effects of molecular behavior of interfacial water on rock surface, high temperature-pressure cell (up to 400 °C and 50 MPa) was developed to measure infrared (IR) and Raman spectra, which was attached with optical microscopy, therefore, in situ and microscopic measurements were enable at high temperature and pressure (HT & HP) conditions. IR spectra of water on metal, interfacial water on quartz surface and synthetic quartz solution were measured. As a result of IR spectroscopic measurements of water on metal, the broad peak at ca. 3400 cm^-1, attributed to OH stretching vibration of water molecules, was observed at high temperature and pressure conditions. Continuous shift of the OH vibration mode was obtained from room to hydrothermal conditions. Compared with the result of IR properties of water on a metal, IR properties of water on a quartz surface exhibit different trend: the peak position shifted to higher wavenumber with increasing temperature and slightly shifted with pressure. IR property of water was changed by environmental conditions such as temperature, pressure and substrate. Molecular structure of interfacial water on the rock and rock-forming mineral at elevated temperatures and pressures were not only changes due to physical conditions such as temperature and pressure but also interaction between water and solid rock materials.