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Measuring the Densities of Aqueous Glasses at Cryogenic Temperatures
Published on: June 28, 2017
Isotope quantum effects in water around the freezing point
1Intense Pulsed Neutron Source Division, Argonne National Laboratory, Argonne, Illinois 60439, USA.
The Journal of Chemical Physics
|April 15, 2006
Summary
The structural isotope effect between heavy water (D2O) and regular water (H2O) significantly increases as temperatures drop below 310 K. This finding challenges simple thermodynamic models at lower temperatures.
Area of Science:
- Physical Chemistry
- Materials Science
- Condensed Matter Physics
Background:
- Understanding the structural differences between water (H2O) and heavy water (D2O) is crucial for various scientific fields.
- Previous studies have explored these differences at higher temperatures.
Purpose of the Study:
- To measure and analyze the electronic structure factor differences between liquid H2O and D2O at low temperatures (268-273 K).
- To compare these findings with existing data and thermodynamic models.
- To evaluate the agreement with quantum molecular dynamics simulations.
Main Methods:
- High-energy X-ray diffraction was employed to measure structural differences.
- Structural isochoric temperature differential and isothermal density differential functions were utilized.
- Comparison with existing experimental data and theoretical simulations.
Main Results:
- The total structural isotope effect between H2O and D2O increases by a factor of 3.5 as temperature decreases over the studied range.
- A simple thermodynamic model accurately describes the structural differences above 310 K but fails at lower temperatures.
- Experimental results show good qualitative agreement with temperature-dependent, rotationally quantized rigid molecule simulations.
Conclusions:
- The structural isotope effect in water is highly temperature-dependent, particularly at lower temperatures.
- Simple thermodynamic models are insufficient to capture the observed structural changes at low temperatures.
- Quantum molecular dynamics simulations provide valuable insights into the behavior of water isotopes.
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