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：7
页码：2458-2463
DOI：10.1073/pnas.1818182116
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：The 2D Raman–terahertz (THz) response of liquid water is studied in dependence of temperature and isotope substitution ( H 2 O, D 2 O, and H 2 18 O). In either case, a very short-lived (i.e., between 75 and 95 fs) echo is observed that reports on the inhomogeneity of the low-frequency intermolecular modes and hence, on the heterogeneity of the hydrogen bond networks of water. The echo lifetime slows down by about 20% when cooling the liquid from room temperature to the freezing point. Furthermore, the echo lifetime of D 2 O is 6.5 ± 1 % slower than that of H 2 O, and both can be mapped on each other by introducing an effective temperature shift of Δ T = 4.5 ± 1 K. In contrast, the temperature-dependent echo lifetimes of H 2 18 O and H 2 O are the same within error. D 2 O and H 2 18 O have identical masses, yet H 2 18 O is much closer to H 2 O in terms of nuclear quantum effects. It is, therefore, concluded that the echo is a measure of the structural inhomogeneity of liquid water induced by nuclear quantum effects.
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