XAFS Study of the Adsorbed Ions onto the Monolayers at Air/Solution Interface

Abstract

Solution surface can be studied by using X-ray Absorption Fine Structure (XAFS) method. To obtain surface sensitivity, the X-rays are introduced onto the solution surface at a very small grazing incidence angle to meet the total-reflection condition. This new spectroscopic method was successfully applied to the surfaces of aqueous solutions covered with monolayers of alkylammonium bromide, zinc stearate, and also zinc porphyrine complex. The spectra from these surfaces indicated quite interesting but not yet known facts such as, dehydration of anions adsorbed onto the alkylammonium monolayer and coordination change of zinc ions from the octahedral to tetrahedral when the metal ions come to the stearate monolayer from the bulk solution. The XAFS experiments were also performed with linearly polarized X-rays to elucidate the selective orientation of the planar Zn porphyrine complex on the solution surface.