Raman H-bond pair volume for water.

Area of Science:

• Physical Chemistry
• Materials Science
• Spectroscopy

Background:

• Water's hydrogen bond network is crucial to its unique properties.
• Understanding pressure-induced structural changes in water is vital for various scientific disciplines.
• Raman spectroscopy provides insights into molecular vibrations and hydrogen bond dynamics.

Purpose of the Study:

• To determine the dispersion of hydrogen bond pair volume (Delta V) in HDO/H2O mixtures.
• To investigate the effect of high pressure on water's hydrogen bond network and volume.
• To correlate spectral features with specific hydrogen bond configurations and their volume changes.

Main Methods:

• Raman spectroscopy was employed to measure spectral intensities of HDO in H2O.
• Measurements were conducted at pressures up to 9700 bar and a constant temperature of 301 K.
• The dispersion of Delta V was calculated using the temperature derivative of Raman intensity ratios with respect to pressure.

Main Results:

• The maximum hydrogen bond pair volume (associated with bond breakage) was determined to be 1.4 ± 0.1 cm³/mol.
• Average Delta V was found to be 0.71 ± 0.10 cm³/mol, indicating significant volume changes upon hydrogen bond alteration.
• Minima in the Delta V dispersion were linked to bent hydrogen bonds ( 150°), and pressure-induced changes favor bent and stronger linear bonds, leading to ice VI formation near 10 kbar.

Conclusions:

• Isothermal pressurization of water leads to a decrease in molal volume by reducing weak, long hydrogen bonds and increasing bent and strong, linear hydrogen bonds.
• These structural modifications are directly linked to the observed phase transitions, such as freezing to ice VI.
• The study provides quantitative data on hydrogen bond volume changes, enhancing our understanding of water's behavior under extreme conditions.