Surface Roughness of Water Measured by X-Ray Reflectivity

The roughness of the liquid-vapor interface for pure water was measured by a technique of x-ray reflectivity. With synchrotron radiation (1. 5 A), the angular dependence of the x-ray reflectivity was measured from grazing incidence (0. 0021 rad), where the reflectivity was greater than 0. 96, to an incident angle of 0. 05 rad, where the reflectivity was 710^-8. A fit to the data by a theory with only one adjustable parameter obtains 3. 2 A for the root-mean-square roughness of the water surface.