A pressure cell for sum frequency generation spectroscopy includes: a metal pressure chamber; a heating stage that heats the liquid sample; a pump, connected to an interior of the metal pressure chamber, that pressurizes the interior of the metal pressure chamber; and a controller that controls the pump and the heating stage to control a pressure of the interior of the metal pressure chamber and a temperature of a liquid sample. The metal pressure chamber includes: a base that retains the liquid sample; a removable lid that seals against the base to enclose the liquid sample in the metal pressure chamber; and a window in the removable lid that exposes the liquid sample to an exterior of the metal pressure chamber.