Extended orientational correlation study for molecular liquids containing distorted tetrahedral molecules:...

Area of Science:

• Molecular dynamics and statistical mechanics
• Physical chemistry and condensed matter physics

Background:

• Existing methods for molecular orientation analysis were limited to perfect tetrahedral molecules.
• Distorted tetrahedral molecules, common in liquids, required a more generalized approach.

Purpose of the Study:

• To extend the Rey method for molecular orientation analysis to distorted tetrahedral molecules of c(2v) symmetry.
• To perform a comprehensive structural determination of methylene halide molecular liquids.

Main Methods:

• Introduction of 28 subgroups to adapt the original six-group analysis for imperfect tetrahedral shapes.
• Derivation of orientational correlation functions and detailed analysis of dipole-dipole correlations.
• Application of calculations to particle configurations from reverse Monte Carlo modeling, validated by diffraction data.

Main Results:

• The most frequent molecular orientation in methylene halide liquids is the 2:2 type across all distances.
• Short-range analysis shows molecules orient via "H,Y"-"H,Y" edges (Y=Cl, Br, I), except for methylene chloride.
• Methylene chloride exhibits a distinct short-range orientation: H,H-H,Cl.

Conclusions:

• The generalized method provides a complete structure determination for molecular systems with distorted tetrahedral molecules.
• Methylene halide liquids exhibit distinct orientational preferences, with methylene chloride differing from methylene bromide and iodide.