Abstract
Elastic fixed window scans of incoherent neutron scattering are an established and frequently employed method to study dynamical changes, usually over a broad temperature range or during a process such as a conformational change in the sample. In particular, the apparent mean-squared displacement can be extracted via a model-free analysis based on a solid physical interpretation as an effective amplitude of molecular motions. Here, we provide a new account of elastic and inelastic fixed window scans, defining a generalized mean-squared displacement for all fixed energy transfers. We show that this generalized mean-squared displacement in principle contains all information on the real mean-square displacement accessible in the instrumental time window. The derived formula provides a clear understanding of the effects of instrumental resolution on the apparent mean-squared displacement. Finally, we show that the generalized mean-square displacement can be used as a model-free indicator on confinement effects within the instrumental time window.
Highlights
The apparent mean-squared displacement (MSD) u2 app determined from elastic fixed window scans of incoherent neutron scattering have been used to explore dynamical changes as a function of parameters such as temperature, pressure, external fields or reaction time
The apparent MSD exploit the general strength of incoherent neutron scattering to explore self-dynamics in confined geometries on molecular length scales
In interpretation, a physical picture of the dynamical changes is obtained by considering the apparent MSD as an effective amplitude of motion, which allows relative comparison between different systems as well as connections to simulational studies
Summary
2 app determined from elastic fixed window scans of incoherent neutron scattering have been used to explore dynamical changes as a function of parameters such as temperature, pressure, external fields or reaction time. The apparent MSD exploit the general strength of incoherent neutron scattering to explore self-dynamics in confined geometries on molecular length scales. In practice, it allows a model-free analysis of the scattering intensity at zero energy transfer, where the scattering intensity is maximal. In interpretation, a physical picture of the dynamical changes is obtained by considering the apparent MSD as an effective amplitude of motion, which allows relative comparison between different systems as well as connections to simulational studies. MSD has been explicitly calculated using a dynamical model for the full quasi-elastic spectra, thereby allowing to separate internal from global dynamics during protein denaturation [18, 19]
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