Neutron scattering in molecular liquids: Influence of orientational degrees of freedom and the prepeak in a fragile glass former

TL;DR

This paper investigates how orientational degrees of freedom affect neutron scattering in molecular liquids, revealing limitations of common analysis methods in supercooled states and clarifying the origin of the prepeak in structure factors.

Contribution

It introduces an expanded representation of the intermediate scattering function for molecular liquids and compares it with simulations, highlighting the failure of Sears-expansion in supercooled regimes.

Findings

Sears-expansion fails in supercooled regimes

The representation clarifies the origin of the prepeak in S(q)

Comparison with MD simulations validates the new approach

Abstract

The intermediate scattering function S(q,t) for neutron scattering is expanded with respect to a complete set of correlation functions which describe the dynamical correlations in a molecular liquid. For the static ns-structure factor S(q) of a system of diatomic molecules the results of the expansion are compared with the exact results from a MD-imulation and it is shown that the Sears-expansion, which is commonly used to interpret such data, fails in the supercooled regime. The representation for S(q) is used to draw conclusions about the q-dependence and especially the origin of the prepeak.