Electronic Properties of Liquid Water in the Vacuum Ultraviolet

Reflectance of liquid water has been measured between 1050 and 3000 Å by two methods, one with the water in an open dish in equilibrium with its vapor and one with a Ca${\mathrm{F}}_2$ or quartz cell. Real and imaginary parts of the index of refraction and dielectric constant, deduced from the data and Fresnel's equations, suggest an exciton transition at 8.3 eV, an interband transition at 9.6 eV, and a band gap of 9 eV.