Raman spectroscopic investigation on pure D2O/H2O from 303 to 573 K: interpretation and implications for water structure

• Published in: Journal of Raman spectroscopy 2017-04, Vol.48 (4), p.610-617
• Main Authors: Hu, Qingcheng, Ouyang, Shunli, Li, Jie, Cao, Zhao
• Format: Article
• Language: English
• Subjects: D2O/H2O structure; high temperature; hydrogen bonding; intermolecular couplings; Raman spectroscopy
• ISSN: 0377-0486; 1097-4555
• DOI: 10.1002/jrs.5088

D2O and H2O structure are investigated by Raman spectroscopy from 303 to 573 K at saturated vapor pressures in a fused silica capillary tube. As temperature increases to 573 K, Raman peak of D2O is blue‐shifted by 93 cm−1, lower than that of H2O by 128 cm−1, but the two Raman shoulders of D2O/H2O nearly remain unchanged in wavenumber. By fitting the spectra into five Gaussian components assigned to water molecules with different hydrogen bonding (HB) environments, these spectral features are interpreted by a mechanism that D2O and H2O have equal types of water molecules with similar HB degrees – fully hydrogen‐bonded H2O/D2O (FHW/D) and partially hydrogen‐bonded H2O/D2O (PHW/D) but distinct HB configurations that O…D–O is more symmetric and stronger than O…H–O. Much smaller values but slightly weaker temperature dependence of full widths at half maxima for D2O spectra ((FWHM)D2O) than (FWHM)H2O are primarily due to much weaker but slightly less temperature‐dependent intermolecular couplings in D2O than in H2O. Enthalpy change (ΔH) and entropy change (ΔS) on transition from FHW/D to PHW/D are determined based on Gaussian fitting. At low temperatures, a higher ΔHD2O (8.62 ± 0.06 kJ mol−1) than ΔHH2O (7.19 ± 0.05 kJ mol−1) further indicates that O…D–O is about 20% stronger than O…H–O. However, difference between O…D–O strength and O…H–O strength tends to diminish above 434 K, suggested by the rather close ΔHD2O and ΔHH2O, and same value of ΔSD2O and ΔSH2O. Copyright © 2017 John Wiley & Sons, Ltd. Raman spectra of D2O and H2O are compared from 303 to 573 K. The spectral features are interpreted that D2O and H2O have equal type of but different structured hydrogen bonding configurations. Much smaller values but slightly weaker temperature dependence of full widths at half maxima for D2O spectra ((FWHM)D2O) than (FWHM)H2O are primarily due to much weaker but slightly less temperature‐dependent intermolecular couplings in D2O than H2O. Enthalpy change and entropy change on structure transition are determined.