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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 V/V 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/2690 cm), which turns into the main peak for the OH (or OD) stretch bands when V/V (or V/V) 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.

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 shift of the C-H symmetric stretching band (v 1 ) of methane can be used to calculate the pressure and density of methane in fluid inclusions. However, previous numerical functions for Raman band shifts and methane density are only suitable for methane with densities lower than 0.3 g/cm 3 . In this study, Raman shifts for pure CH 4 were systematically measured at 25 ºC and pressures up to 150 MPa. Parameters of the long range attractive forces were fitted, and Raman shifts of CH 4 were calculated with hard sphere model for density up to 0.55 g/cm 3 . Based on experimental data and theoretical calculation, a unified equation was established to calculate the density of methane gas from Raman shifts over a wide density ranges up to 0.55 g/cm 3 :Where represents the density of methane in g/cm 3 ;is the difference between the meaured 23 peak position of methane in the fluid inclusion ( ) and the known peak position of methane at quite 24 low density ( ). The equation will work regardless of which machine the measurements of Raman 25 shifts are done on, as long as the user knows or finds the zero-density peak position. 26 Hansen et al., 2001; Lin et al., 2007; Lu et al., 2007). 40 Lu et al. (2007) established a unified equation for calculating methane pressures in the 41 CH 4 -H 2 O system from Raman shifts for the C-H symmetric stretching band of methane. However, 42 the pressure range of most previous measurements is just from 0 to 70 MPa, and the corresponding 43 methane densities are lower than 0.3 g/cm 3 , so their equations do not apply to the inclusions with 44 density higher than 0.3 g/cm 3 . 45In this study, we measured Raman shifts of pure methane at pressures up to 150 MPa at 25 ºC. 46 With the new data and theoretical calculation, we established an equation which could be also 47 applied in other laboratories for determining the density of methane in pure CH 4 fluid inclusions. The 48 new equation was effectively applied to determine the density of four typical pure CH 4 inclusions in 49 two samples obtained from a MVT-Pb-Zn deposit in mid-south China. 50 2. Methods 51 2.1 Experimental apparatus and procedures 52 4 The apparatus and procedures are similar to those used in the study of Lu et al. (2007) (Fig. 1). 53Experiments were carried out with a capillary high-pressure optical cell (HPOC; Chou et al., 1990 Chou et al., , 54 2005. After the capillary cell and pipeline were evacuated, methane (99.99%, Air Products) was 55 loaded into the cell and Raman spectra were collected under high pressures gradually up to 150 MPa. 56The methane pressure in the optical cell was adjusted by a high pressure generator and monitored by 57 an Omega PX91N0-50KSV digital pressure transducer (on a full scale of 400 MPa, accurate to ± 0.5 58 %). The temperature in the cell was controlled by a Linkam CAP 500 heating-cooling stage with an 59 accuracy of ± 0.1 ºC at 25 ºC (Lu et al., 2013). 60 Spectra collection and calibration 61Raman spectra of gas were collected with a JY/Horiba LabRam HR 800 system provided with 62...

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