Adsorption at the Liquid Surface
Molecules with a lower surface energy tend to accumulate at the liquid/air surface. The adsorbed amount is normally determined though measurements of the surface tension as a function of solute concentration. The state of the molecule can only be determined through spectroscopy.
In this novel technique the liquid surface is illuminated with two light beams with different frequency. The output beam, which frequency equals the sum of the two incoming beams, carries information on the composition, orientation and structure information of the molecules at the surface.