A high-quality x-ray scattering experiment on liquid water at ambient conditions

TLDR

The study reports a new, high‑quality x‑ray scattering experiment on pure ambient water performed at the Advanced Light Source synchrotron beam line. The experiment employed a highly monochromatic synchrotron source, precise polarization and Compton scattering corrections (including electron correlation), a modern CCD detector, and a detailed data‑processing pipeline to correct systematic errors and quantify remaining random errors. The resulting data exhibit smaller error estimates than previous experiments, revealing that the current scattering curves favor a gOO(r) with a first peak of 2.8 and systematically shifted peak positions compared to older data that suggested a 2.2 peak height.

Abstract

We report a new, high-quality x-ray scattering experiment on pure ambient water using a synchrotron beam line at the Advanced Light Source at Lawrence Berkeley National Laboratory. Several factors contribute to the improved quality of our intensity curves including use of a highly monochromatic source, a well-characterized polarization correction, a Compton scattering correction that includes electron correlation, and more accurate intensities using a modern charge coupled device (CCD) detector. We provide a comprehensive description of the data processing that we have used for correcting systematic errors, and we provide an estimate of our remaining random errors. The resulting error estimates of our data are smaller then the discrepancies between data sets collected in past x-ray experiments. We find that the older x-ray curves support a family of gOO(r)’s that exhibit a smaller first peak (∼2.2), while the current data is better fit with a family of gOO(r)’s with a first peak height of 2.8, and systematic shifts in all peak positions to smaller r.