Electric Fields, Reorientation, and Water at the Air-water Interface of Iron and other Salt Solutions*

Water at the air-water interface organizes and facilitates the accommodation of ion complexes and that of surface active species. The hydration shells of these surface active components are evident by their spectroscopic signatures mostly in the OH stretching regions using both vibrational sum frequency generation and infrared reflection absorption spectroscopies. In addition, surface potential measurements reveal information on the interfacial electric field strength and thus ordering of molecular and ion complexation dipoles in the interfacial region. We report evidence of interfacial iron (III) speciation and other ions and their interfacial hydration effects. We also report on the resistance to dipole reorientation of ion and molecular species at the air-aqueous interface of iron(III) sulfate and nitrate versus iron(III) chloride.