Optical Measurements of Liquid Water in the Vacuum Ultraviolet

Two methods have been used to determine the optical and dielectric properties of liquid water in the vacuum ultraviolet. In the first, the reflectance of water in equilibrium with its vapor at 1°C was measured in the spectral region from 3000 to 1050 Å for three angles of incidence. In the second, water was placed against the plane surface of a transparent semicylinder, which formed one side of a sealed cell, and the reflectance was measured at the water–semicylinder interface. Real and imaginary parts of the complex index of refraction and dielectric constant were deduced from the data and Fresnel's equations. Peaks in the complex dielectric constant occur at 8.3 and 9.6 eV. Though the absorption bands cannot at present be unambiguously assigned, possible mechanisms to explain the ultraviolet structure are presented.