The interaction of water vapor with NaCl crystallites at 240 and 296 K has been studied through Fourier transform infrared spectroscopy. Water not only physically adsorbs to the surface to form an adlayer but also dissociates on defects at the surface. Water dissociation occurs in less than 1% of ah available surface sites of the crystallites and results in the production of hydroxide anions which are bound at the surface. For the first time, the infrared vibrational spectra of surface OH- has been observed and has a frequency of 3667 cm(-1). It has also been demonstrated that the surface OH- infrared spectra are sensitive to temperature and foreign adsorbed molecules such as hydrogen.