Ionization of Solute Molecules at the Liquid Water Surface, Interfaces, and Self-Assembled Systems

Studies on the photoionization measurements of solute molecules adsorbed at the liquid water surface are summarized for the molecular -level understanding at the surface. Interface selective observation methods are overlooked with a view point of detection sensitivity. It is pointed out that a photoionization measurement with moderate sensitivity, fine surface selectivity, and good applicability is an attractive technique for observing solute molecules at the water surface. The methods for measurements of photoionization current spectra, laser multi-photon ionization current, laser second harmonic generation and surface tension are described. Some discussion on photoionization thresholds, polarization- and concentration dependence, and surface molecular monitoring are presented of surface-adsorbed molecules, based on experimental data.