Neutron scattering of residual hydrogen in 1,4-dioxane d8 liquid: Understanding measurements with molecular dynamics simulations
Abstract
That incoherent scattering from protiated molecular liquids adds a constant background to the measured scattering intensity is well-known, but less appreciated is the fact that coherent scattering is also induced by the presence of hydrogen in a deuterated liquid. In fact, the scattering intensity can be very sensitive, in the small-q region, with respect to the amounts and distribution of residual H in the system. We used 1,4-dioxane liquid to demonstrate that the partial structure factors of the HD and DD atom pairs contribute significantly to intermolecular scattering and that uncertainty in the extent of deuteration account for discrepancies between simulations and measurements. Both contributions to uncertainty have similar magnitudes: scattering interference of the hydrogen–deuterium pair, and complementary interference from the deuterium–deuterium pair by virtue of chemical inhomogeneity. This situation arises in practice since deuteration of liquids is often 99% or less. A combined experimental and extensive computational study of static thermal neutron scattering of 1,4-dioxane demonstrates the foregoing. We show, through simulations, that the reason for the differences is the content of protiated dioxane (vendors quote 1%). We estimate that up to 5% (at 298 K and at 343 K) protiated molar fraction may be involved in generating themore »
- Authors:
-
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
- Publication Date:
- Research Org.:
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Spallation Neutron Source (SNS)
- Sponsoring Org.:
- USDOE Laboratory Directed Research and Development (LDRD) Program
- OSTI Identifier:
- 1261561
- Grant/Contract Number:
- AC05-00OR22725
- Resource Type:
- Accepted Manuscript
- Journal Name:
- Journal of Physical Chemistry. B, Condensed Matter, Materials, Surfaces, Interfaces and Biophysical Chemistry
- Additional Journal Information:
- Journal Volume: 120; Journal Issue: 24; Journal ID: ISSN 1520-6106
- Publisher:
- American Chemical Society
- Country of Publication:
- United States
- Language:
- English
- Subject:
- 75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY
Citation Formats
Liu, Hongjun, Herwig, Kenneth W., Kidder, Michelle K., and de Almeida, Valmor F.. Neutron scattering of residual hydrogen in 1,4-dioxane d8 liquid: Understanding measurements with molecular dynamics simulations. United States: N. p., 2016.
Web. doi:10.1021/acs.jpcb.6b00872.
Liu, Hongjun, Herwig, Kenneth W., Kidder, Michelle K., & de Almeida, Valmor F.. Neutron scattering of residual hydrogen in 1,4-dioxane d8 liquid: Understanding measurements with molecular dynamics simulations. United States. https://doi.org/10.1021/acs.jpcb.6b00872
Liu, Hongjun, Herwig, Kenneth W., Kidder, Michelle K., and de Almeida, Valmor F.. Wed .
"Neutron scattering of residual hydrogen in 1,4-dioxane d8 liquid: Understanding measurements with molecular dynamics simulations". United States. https://doi.org/10.1021/acs.jpcb.6b00872. https://www.osti.gov/servlets/purl/1261561.
@article{osti_1261561,
title = {Neutron scattering of residual hydrogen in 1,4-dioxane d8 liquid: Understanding measurements with molecular dynamics simulations},
author = {Liu, Hongjun and Herwig, Kenneth W. and Kidder, Michelle K. and de Almeida, Valmor F.},
abstractNote = {That incoherent scattering from protiated molecular liquids adds a constant background to the measured scattering intensity is well-known, but less appreciated is the fact that coherent scattering is also induced by the presence of hydrogen in a deuterated liquid. In fact, the scattering intensity can be very sensitive, in the small-q region, with respect to the amounts and distribution of residual H in the system. We used 1,4-dioxane liquid to demonstrate that the partial structure factors of the HD and DD atom pairs contribute significantly to intermolecular scattering and that uncertainty in the extent of deuteration account for discrepancies between simulations and measurements. Both contributions to uncertainty have similar magnitudes: scattering interference of the hydrogen–deuterium pair, and complementary interference from the deuterium–deuterium pair by virtue of chemical inhomogeneity. This situation arises in practice since deuteration of liquids is often 99% or less. A combined experimental and extensive computational study of static thermal neutron scattering of 1,4-dioxane demonstrates the foregoing. We show, through simulations, that the reason for the differences is the content of protiated dioxane (vendors quote 1%). We estimate that up to 5% (at 298 K and at 343 K) protiated molar fraction may be involved in generating the scattering differences. Finally, we find that the particular distribution of hydrogen in the protiated molecules affects the results significantly; here, we considered molecules to be either fully protiated or fully deuterated. This scenario best reconciles the computational and experimental results, and leads us to speculate that the deuteration synthesis process tends to leave a molecule either fully deuterated or fully protiated. As a result, we have used 1,4-dioxane as a model liquid, the effects described in this study extend to similar liquids, and similar systematic experimental/computational studies can be performed to either understand measurements or calibrate/validate molecular dynamics models.},
doi = {10.1021/acs.jpcb.6b00872},
journal = {Journal of Physical Chemistry. B, Condensed Matter, Materials, Surfaces, Interfaces and Biophysical Chemistry},
number = 24,
volume = 120,
place = {United States},
year = {2016},
month = {6}
}
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