Vibrational couplings and line shapes of CN stretchings in aqueous KOCN-KSCN binary systems in two-dimensional layers

Abstract

Infrared spectra in the region of the CN stretchings of aqueous KOCN-KSCN binary systems as well as KOCN or KSCN pure solutions are observed in the gel phase of the mono-palmitin-water system, where two-dimensional water layers are formed. Similar observations are carried out for the systems with sodium dodecyl sulphate (SDS). The spectra are analyzed on the basis of a linear response function with mechanical and damping coupling constants. In the KOCN or KSCN pure solutions the band widths depend slightly on SDS and differ considerably with those in the isotropic solutions, clarifying the difference in the correlation time of water between the two-dimensional and the isotropic systems. In the KOCN–KSCN binary systems the relative intensities of the OCN − with SCN − ions depend considerably on SDS. This is explained in terms of the orientation of OCN − ions, which prefer to orient parallel to the water-lipid boundary. The mechanical coupling constant is somewhat larger than that expected from two-dimensional layers. This results in the effects of both the reduction of a dielectric constant of water and multiple reflections of an electric field on the water-lipid boundary.