%0 Journal Article
%T Cross-correlation analysis of X-ray photon correlation spectroscopy to extract rotational diffusion coefficients.
%A Hu Z
%A Donatelli JJ
%A Sethian JA
%J Proc Natl Acad Sci U S A
%V 118
%N 34
%D 08 2021 24
%M 34408023
%F 12.779
%R 10.1073/pnas.2105826118
%X Coefficients for translational and rotational diffusion characterize the Brownian motion of particles. Emerging X-ray photon correlation spectroscopy (XPCS) experiments probe a broad range of length scales and time scales and are well-suited for investigation of Brownian motion. While methods for estimating the translational diffusion coefficients from XPCS are well-developed, there are no algorithms for measuring the rotational diffusion coefficients based on XPCS, even though the required raw data are accessible from such experiments. In this paper, we propose angular-temporal cross-correlation analysis of XPCS data and show that this information can be used to design a numerical algorithm (Multi-Tiered Estimation for Correlation Spectroscopy [MTECS]) for predicting the rotational diffusion coefficient utilizing the cross-correlation: This approach is applicable to other wavelengths beyond this regime. We verify the accuracy of this algorithmic approach across a range of simulated data.