Neutron scattering and molecular correlations in a supercooled liquid

Abstract

We show that the intermediate scattering function $S_n(q,t)$ for neutron scattering (ns) can be expanded naturely with respect to a set of molecular correlation functions that give a complete description of the translational and orientational two-point correlations in the liquid. The general properties of this expansion are discussed with special focus on the $q$-dependence and hints for a (partial) determination of the molecular correlation functions from neutron scattering results are given. The resulting representation of the static structure factor $S_n(q)$ is studied in detail for a model system using data from a molecular dynamics simulation of a supercooled liquid of rigid diatomic molecules. The comparison between the exact result for $S_n(q)$ and different approximations that result from a truncation of the series representation demonstrates its good convergence for the given model system. On the other hand it shows explicitly that the coupling between translational (TDOF) and orientational degrees of freedom (ODOF) of each molecule and rotational motion of different molecules can not be neglected in the supercooled regime.Further we report the existence of a prepeak in the ns-static structure factor of the examined fragile glassformer, demonstrating that prepeaks can occur even in the most simple molecular liquids. Besides examining the dependence of the prepeak on the scattering length and the temperature we use the expansion of $S_n(q)$ into molecular correlation functions to point out intermediate range orientational order as its principle origin.

13 pages, 7 figures

References in corpus (4)

• Dynamics of the rotational degrees of freedom in a supercooled liquid of diatomic molecules
• Experimental Indication of Structural Heterogeneities in Fragile Hydrogen-bonded Liquids
• Test of mode coupling theory for a supercooled liquid of diatomic molecules.I. Translational degrees of freedom
• Test of mode coupling theory for a supercooled liquid of diatomic molecules. II. q-dependent orientational correlators

Cited by in corpus (7)

• Neutron Scattering Studies of the Model Glass Former Ortho-terphenyl
• Molecular mode-coupling theory for supercooled liquids: Application to water
• Structural relaxation in supercooled orthoterphenyl
• Molecular mode-coupling theory applied to a liquid of diatomic molecules
• Microscopic dynamics of molecular liquids and glasses: Role of orientations and translation-rotation coupling
• Experimental and numerical signatures of dynamical crossover in orientationally disordered crystals
• Microscopic theory of glassy dynamics and glass transition for molecular crystals