期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2019
卷号：116
期号：35
页码：17156-17157
DOI：10.1073/pnas.1905756116
出版社：The National Academy of Sciences of the United States of America
摘要：Ambient water properties have been shown to require heterogeneity (1). Niskanen et al. (2) apply a linear relationship between the intensity of the 4a1 excitation in an electron energy loss spectroscopy gas-phase spectrum and the preedge in water and ice from X-ray Raman scattering to extract the number of hydrogen bonds (HBs) and conclude about homogeneity of liquid water. We raise several concerns regarding their analysis and interpretation. First, an HB number by itself cannot say anything about homogeneity or heterogeneity since one needs to determine the spatial distribution. Second, due to extended X-ray absorption fine structure oscillations (3) and energy-dependent shake-off processes, normalization by the f-sum rule requires measurements extended to 500 eV above the edge, and not.
