Observation of molecular reorientation at a two-dimensional-liquid phase transition

Abstract
The structure of a monolayer of pentadecanoic acid near the liquid-expandedliquid-condensed phase transition at a water-air interface is studied by optical second-harmonic generation. The results show that this transition is accompanied by a reorientation of the molecules and that the two phases are separated by an inhomogeneous coexistence region on the isotherms.