While many vibrational Raman spectroscopy studies of liquid water have investigated the temperature dependence of the high-frequency O-H stretching region, few have analyzed the changes in the Raman spectrum as a function of temperature over the entire spectral range. Here, we obtain the Raman spectra of water from its melting to boiling point, both experimentally and from simulations using an ab initio-trained machine learning potential. We use these to assign the Raman bands and show that the entire spectrum can be well described as a combination of two temperature-independent spectra. We then assess which spectral regions exhibit strong dependence on the local tetrahedral order in the liquid. Further, this work demonstrates that changes in this structural parameter can be used to elucidate the temperature dependence of the Raman spectrum of liquid water and provides a guide to the Raman features that signal water ordering in more complex aqueous systems.

Charles University Faculty of Mathematics and Physics Ke Karlovu 3 121 16 Prague 2 Czech Republic

Department of Chemistry Purdue University West Lafayette Indiana 47907 United States

Department of Chemistry Stanford University Stanford California 94305 United States

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Weakly hydrated anions bind to polymers but not monomers in aqueous solutions