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

Abstract

D 2 O and H 2 O 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 D 2 O is blue‐shifted by 93 cm −1 , lower than that of H 2 O by 128 cm −1 , but the two Raman shoulders of D 2 O/H 2 O 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 D 2 O and H 2 O have equal types of water molecules with similar HB degrees – fully hydrogen‐bonded H 2 O/D 2 O (FHW/D) and partially hydrogen‐bonded H 2 O/D 2 O (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 D 2 O spectra ((FWHM) D2O ) than (FWHM) H2O are primarily due to much weaker but slightly less temperature‐dependent intermolecular couplings in D 2 O than in H 2 O. Enthalpy change (Δ H ) and entropy change (Δ S ) on transition from FHW/D to PHW/D are determined based on Gaussian fitting. At low temperatures, a higher Δ H D2O (8.62 ± 0.06 kJ mol −1 ) than Δ H H2O (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 Δ H D2O and Δ H H2O , and same value of Δ S D2O and Δ S H2O . Copyright © 2017 John Wiley & Sons, Ltd.