Full description of the orientational statistics of molecules near to interfaces. Water at the interface with CCl4

Abstract

The orientational statistics of water molecules at the vicinity of the water/CCl₄ liquid–liquid interface is analyzed at different levels of statistics on the basis of a Monte Carlo computer simulation. Profiles describing the average orientation of various molecule-fixed vectors relative to the interface along the interface normal axis, monovariate distributions of parameters describing these orientations, as well as the bivariate joint probability distribution of two independent orientational parameters in different water layers are determined. It is demonstrated that a complete description of the orientational preferences of the entire water molecule can only be given by the bivariate joint probability distribution of two independent orientational parameters. Two co-existing preferred orientations of the water molecules have found: in the first orientation, present at the entire interfacial region, the water molecule lays in a plane parallel with the interface, whereas in the second preferred orientation, present only among the water molecules penetrated deepest into the nonpolar phase, the plane of the water molecule is perpendicular to the interface and one of its O–H bonds points straight toward the nonpolar phase. This latter orientation corresponds to the orientation expected for a hydrogen bonded neighbor, located toward the nonpolar phase, of a water molecule which lays parallel with the interface.