Mid-IR spectroscopy of supercritical water: From dilute gas to dense fluid

Mixed quantum-classical methods are commonly used to calculate infrared spectra for condensed-phase systems. These methods have been applied to study water in a range of conditions from liquid to solid to supercooled. Here, we show that these methods also predict infrared line shapes in excellent ag...

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Bibliographic Details
Published in:The Journal of chemical physics 2019-02, Vol.150 (5), p.054505-054505
Main Authors: Hestand, Nicholas J., Strong, Steven E., Shi, Liang, Skinner, J. L.
Format: Article
Language:English
Subjects:
Classical mechanics
Dilution
Infrared spectra
Infrared spectroscopy
Line shape
Percolation
Physics
Spectrum analysis
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Summary:Mixed quantum-classical methods are commonly used to calculate infrared spectra for condensed-phase systems. These methods have been applied to study water in a range of conditions from liquid to solid to supercooled. Here, we show that these methods also predict infrared line shapes in excellent agreement with experiments in supercritical water. Specifically, we study the OD stretching mode of dilute HOD in H2O. We find no qualitative change in the spectrum upon passing through the near-critical region (Widom line) or the hydrogen-bond percolation line. At very low densities, the spectrum does change qualitatively, becoming rovibrational in character. We describe this rovibrational spectrum from the perspective of classical mechanics and provide a classical interpretation of the rovibrational line shape for both HOD and H2O. This treatment is perhaps more accessible than the conventional quantum-mechanical treatment.
ISSN:0021-9606
1089-7690
DOI:10.1063/1.5079232