Salt-induced Long-to-Short Range Orientational Transition in Water.

We report the long-range orientational organization of water using polarization-resolved second harmonic scattering operated in a right-angle configuration. A transition is observed between the neat water orientational organization involving an azimuthal molecular orientation distribution towards a radial molecular orientation distribution when salt is added. These two orientational phases are quantitatively described using a molecular model of the second harmonic scattering response. It is observed that the long-range correlation present in the neat water phase abruptly disappears and is replaced by a shorter range correlation centered around the ions as the salt concentration is increased.