The Liquid Vapour Interface

In this short review we are concerned with the density variation across the liquid-vapour interface, i.e. from the bulk density of the liquid to the essentially zero density of the vapour phase. This density variation can in principle be determined from the deviation of the reflectivity from Fresnel's law for incidence angles larger than the critical angle for total reflection. However, in this range the reflectivity may typically have dropped by 7 or 8 order of magnitude from its value below the critical angle, and therefore the availability of intense synchrotron radiation sources have made such measurements practically feasible.