OVERVIEW OF PREVIOUS STUDIES i.) No particular orientational preference Carpenter, Hehre, JPC 94 (1990) 531 hexane ii.) Dipole of water molecules located -closest to the apolar phase points toward the apolar phase -farther from the apolar phase points toward the aqueous phase van Buuren et al., JPC 97 (1993) 9206 decane iii.) Dipole of water molecules is parallel with the interface Linse, JCP 86 (1987) 417, benzene Benjamin, JCP 97 (1992) 1432 1,2-dichloroethane iv.) Dipole of water molecules is almost parallel with the interface, however, it deviates from parallel alignment -toward the apolar rather than the aqueous phase for waters located closest to the apolar phase -toward the aqueous rather than the apolar phase for waters located farther from the apolar phase Zhang et al., JCP 103 (1995) 10252, octane Fernandes et al., JPC/B 103 (1999) 6290 2-heptanone
v.) The H-H vector of the water molecules located closest to the interface is perpendicular to the interface Benjamin, JCP 97 (1992) 1432 1,2-dichloroethane Chang and Dang, JCP 104 (1996) 6772 CCl 4 Vincze et al., Anal. Sci. 17 (2001) i317 1,2-dichloroethane vi.) The H-H vector of the water molecules located farther from the interface has no particular orientational preference Benjamin, JCP 97 (1992) 1432 1,2-dichloroethane vii.) The H-H vector of the water molecules located farther from the interface is parallel with the interface Chang and Dang, JCP 104 (1996) 6772 CCl 4
1. Level of the orientational profiles of various orientational parameters Average of parameters describing the orientation of various, molecule-fixed vectors relative to the interface – irrespective the other vectors Profiles along the interface normal 2. Level of monovariate distributions of the individual orientational parameters Distribution of these parameters in separate water layers along the interface normal 3. Level of bivariate distribution of two independent orientational parameters Joint distribution of two independent orientational parameters in separate water layers along the interface normal. (One to one mapping of orientation on the parameters not sufficient. Distribution in bulk should be uniform!) Concept of the bivariate joint distributions The interfacial orientation of the molecules can be analyzed at different levels of statistics:
Orientációs eloszlási térképek a felszínközeli rétegekben X I II
Non-equilibrium dynamics and structure of interfacial ice Oliviero Andreussi, Davide Donadio, Michele Parrinello, Ahmed H. Zewail Chemical Physics Letters 2006 Figure 4 Orientational probability distribution P(cos θ, φ) for the three regions of three bilayer thick interfacial ice. The two independent orientational parameters (θ, φ) are the angular polar coordinates of the vector normal to the substrate's surface, in a coordinate frame fixed to the individual water molecules . The presence of four preferred orientations is evident for the crystalline systems (below 180 K). At higher temperatures systems present orientational disorder in the bulk region, while molecules at the free surface tend to point towards the inner layers and a more structured bilayer is present at the ice-substrate interface
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