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Issue 32, 2017
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Understanding water structure from Raman spectra of isotopic substitution H2O/D2O up to 573 K

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Abstract

The OH/OD stretch band on Raman spectra of water is complex, and understanding the spectral features based on water structure needs further study. This study investigates Raman spectra of isotopic substitution (IS) of water (with volume ratio VH2O/VD2O of 0/1, 1/4, 1/1, 4/1 and 1/0) at temperatures from 303 to 573 K. The data show that the OH and OD stretch band profiles are similar in their dependences on temperature and IS ratio. IS reduces the band widths at low temperatures but the reducing effect diminishes above ∼450 K, due to the largely enhanced intensity of the high-frequency shoulder (∼3650 cm−1/2690 cm−1), which turns into the main peak for the OH (or OD) stretch bands when VH2O/VD2O (or VD2O/VH2O) reaches 1/4 at temperatures over ∼510 K. These spectral features strongly indicate a multi-structure model stating that water has various local hydrogen bonding (HB) environments. Intermolecular vibrational couplings are important in determining the band width, while intramolecular vibrational couplings are not recommended for interpreting the OH/OD stretch band. Five dominant HB configurations are identified in water: two types of tetrahedral, single donor (SD) HB configuration, single hydrogen-bonded water (SHW), and free water (FW) without any hydrogen bonds, which are represented by five sub-bands. It is estimated that most (>50%) of the water molecules are in highly asymmetric HB environments (SD and SHW). The increase of temperature breaks HB structure and IS further promotes structure transition from tetrahedral to SD, SHW and FW. Then, number of hydrogen bonds in water are greatly reduced by temperature and IS.

Graphical abstract: Understanding water structure from Raman spectra of isotopic substitution H2O/D2O up to 573 K

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Publication details

The article was received on 31 Mar 2017, accepted on 19 Jul 2017 and first published on 20 Jul 2017


Article type: Paper
DOI: 10.1039/C7CP02065A
Citation: Phys. Chem. Chem. Phys., 2017,19, 21540-21547
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    Understanding water structure from Raman spectra of isotopic substitution H2O/D2O up to 573 K

    Q. Hu, H. Zhao and S. Ouyang, Phys. Chem. Chem. Phys., 2017, 19, 21540
    DOI: 10.1039/C7CP02065A

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