POLARIZATION OF WATER-MOLECULES AT A CHARGED INTERFACE - 2ND HARMONIC STUDIES OF CHARGED MONOLAYERS AT THE AIR-WATER-INTERFACE

The second harmonic generation from charged monolayers at air/water interfaces is shown to be linearly related to the interface electric potential. This dependence is due to the polarization of water molecules in the electrostatic field of the charged monolayer. The observed linear dependence of the second harmonic field on the interface electric potential serves as the basis of a proposed method for obtaining the interface potential, which it should be noted is a nonintrusive optical method. The work presented here also indicates that the Gouy-Chapman model is valid at the air/water charged interface up to at least a 1 M total electrolyte concentration.