skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Molecular Dynamics Simulations of the Solution-Air Interface of Aqueous Sodium Nitrate

Abstract

Molecular dynamics simulations have been used to investigate the behavior of aqueous sodium nitrate in interfacial environments. Polarizable potentials for the water molecules and the nitrate ion in solution were employed. Calculated surface tension data at several concentrations are in good agreement with measured surface tension data. The surface potential of NaNO3 solutions at two concentrations also compare favorably with experimental measurements. Density profiles suggest that NO3 - resides primarily below the surface of the solutions over a wide range of concentrations. When the nitrate anions approach the surface of the solution, they are significantly undercoordinated compared to in the bulk, and this may be important for reactions where solvent cage effects play a role, such as photochemical processes. Surface water orientation is perturbed by the presence of nitrate ions, and this has implications for experimental studies that probe interfacial water orientation. Nitrate ions near the surface also have a preferred orientation that places the oxygen atoms in the plane of the interface. The availability of NO3 - for reaction at the surface of aerosols in the atmosphere is discussed. The work at Pacific Northwest National Laboratory was performed under the auspices of the Division of Chemical Sciences, Office ofmore » Basic Energy Sciences, U.S. Department of Energy. Pacific Northwest National Laboratory is operated by Battelle for the Department of Energy.« less

Authors:
; ; ;
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
909472
Report Number(s):
PNNL-SA-53223
KC0301020; TRN: US200722%%1100
DOE Contract Number:
AC05-76RL01830
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Physical Chemistry A, 111(16):3091-3098; Journal Volume: 111; Journal Issue: 16
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; AEROSOLS; SODIUM NITRATES; SURFACE POTENTIAL; SURFACE TENSION; SURFACE WATERS; MOLECULAR DYNAMICS METHOD; AIR-WATER INTERACTIONS; AQUEOUS SOLUTIONS; INTERFACES; ATMOSPHERIC CHEMISTRY

Citation Formats

Thomas, Jennie L., Roeselova, Martina, Dang, Liem X., and Tobias, Douglas J.. Molecular Dynamics Simulations of the Solution-Air Interface of Aqueous Sodium Nitrate. United States: N. p., 2007. Web. doi:10.1021/jp0683972.
Thomas, Jennie L., Roeselova, Martina, Dang, Liem X., & Tobias, Douglas J.. Molecular Dynamics Simulations of the Solution-Air Interface of Aqueous Sodium Nitrate. United States. doi:10.1021/jp0683972.
Thomas, Jennie L., Roeselova, Martina, Dang, Liem X., and Tobias, Douglas J.. Thu . "Molecular Dynamics Simulations of the Solution-Air Interface of Aqueous Sodium Nitrate". United States. doi:10.1021/jp0683972.
@article{osti_909472,
title = {Molecular Dynamics Simulations of the Solution-Air Interface of Aqueous Sodium Nitrate},
author = {Thomas, Jennie L. and Roeselova, Martina and Dang, Liem X. and Tobias, Douglas J.},
abstractNote = {Molecular dynamics simulations have been used to investigate the behavior of aqueous sodium nitrate in interfacial environments. Polarizable potentials for the water molecules and the nitrate ion in solution were employed. Calculated surface tension data at several concentrations are in good agreement with measured surface tension data. The surface potential of NaNO3 solutions at two concentrations also compare favorably with experimental measurements. Density profiles suggest that NO3 - resides primarily below the surface of the solutions over a wide range of concentrations. When the nitrate anions approach the surface of the solution, they are significantly undercoordinated compared to in the bulk, and this may be important for reactions where solvent cage effects play a role, such as photochemical processes. Surface water orientation is perturbed by the presence of nitrate ions, and this has implications for experimental studies that probe interfacial water orientation. Nitrate ions near the surface also have a preferred orientation that places the oxygen atoms in the plane of the interface. The availability of NO3 - for reaction at the surface of aerosols in the atmosphere is discussed. The work at Pacific Northwest National Laboratory was performed under the auspices of the Division of Chemical Sciences, Office of Basic Energy Sciences, U.S. Department of Energy. Pacific Northwest National Laboratory is operated by Battelle for the Department of Energy.},
doi = {10.1021/jp0683972},
journal = {Journal of Physical Chemistry A, 111(16):3091-3098},
number = 16,
volume = 111,
place = {United States},
year = {Thu Apr 26 00:00:00 EDT 2007},
month = {Thu Apr 26 00:00:00 EDT 2007}
}
  • Many experimental and theoretical studies have established the specific anion, as well as cation effects on the hydrogen-bond structures at the air/water interface of electrolyte solutions. However, the ion effects on the top-most layer of the air/water interface, which is signified by the non-hydrogen-bonded so-called ‘free O-H’ group, has not been discussed or studied. In this report, we present the measurement of changes of the orientational angle of the ‘free O-H’ group at the air/water interface of the sodium fluoride (NaF) solutions at different concentrations using the interface selective sum-frequency generation vibrational spectroscopy (SFG-VS) in the ssp and ppp polarizations.more » The polarization dependent SFG-VS results show that the average tilt angle of the ‘free O-H’ changes from about 35.3 degrees ± 0.5 degrees to 43.4 degrees ± 2.1degrees as the NaF concentration increase from 0 to 0.94M (nearly saturated). Such tilt angle change is around the axis of the other O-H group of the same water molecule at the top-most layer at the air/water interface that is hydrogen-bonded to the water molecules below the top-most layer. These results provide quantitative molecular details of the ion effects of the NaF salt on the structure of the water molecules at the top-most layer of the air/water interfacial, even though both the Na+ cation and the F- anion are believed to be among the most excluded ions from the air/water interface.« less
  • Ab initio molecular dynamics simulations were employed to investigate, with explicit solvent water molecules, {beta}-d-glucose and {beta}-d-xylose degradation mechanisms in acidic media. The rate-limiting step in sugar degradation was found to be protonation of the hydroxyl groups on the sugar ring. We found that the structure of water molecules plays a significant role in the acidic sugar degradation pathways. Firstly, a water molecule competes with the hydroxyl group on the sugar ring for protons. Secondly, water forms hydrogen bonds with the hydroxyl groups on the sugar rings, thus weakening the C-C and C-O bonds (each to a different degree). Notemore » that the reaction pathways could be altered due to the change of relative stability of the C-C and C-O bonds. Thirdly, water molecules that are hydrogen-bonded to sugar hydroxyls could easily extract a proton from the reaction intermediate, terminating the reaction. Indeed, the sugar degradation pathway is complex due to multiple protonation probabilities and the surrounding water structure. Our experimental data support multiple sugar acidic degradation pathways.« less
  • Car-Parrinello molecular dynamics (CPMD) simulations have been used to examine the hydration structures, coordination energetics and the first hydrolysis constants of Pu3+, Pu4+, PuO2+ and PuO22+ ions in aqueous solution at 300 K. The coordination numbers and structural properties of the first shell of these ions are in good agreement with available experimental estimates. The hexavalent PuO22+ species is coordinated to 5 aquo ligands while the pentavalent PuO2+ complex is coordinated to 4 aquo ligands. The Pu3+ and Pu4+ ions are both coordinated to 8 water molecules. The first hydrolysis constants obtained for Pu3+ and PuO22+ are 6.65 and 5.70more » respectively, all within 0.3 pH units of the experimental values (6.90 and 5.50 respectively). The hydrolysis constant of Pu4+, 0.17, disagrees with the value of -0.60 in the most recent update of the Nuclear Energy Agency Thermochemical Database (NEA-TDB) but supports recent experimental findings. The hydrolysis constant of PuO2+, 9.51, supports the experimental results of Bennett et al. (Radiochim. Act. 1992, 56, 15). A correlation between the pKa of the first hydrolysis reaction and the effective charge of the plutonium center was found.« less
  • On-the-fly excited-state quantum mechanics/molecular mechanics molecular dynamics (QM/MM-MD) simulations of thymine in aqueous solution are performed to investigate the role of solvent water molecules on the nonradiative deactivation process. The complete active space second-order perturbation theory (CASPT2) method is employed for a thymine molecule as the QM part in order to provide a reliable description of the excited-state potential energies. It is found that, in addition to the previously reported deactivation pathway involving the twisting of the C-C double bond in the pyrimidine ring, another efficient deactivation pathway leading to conical intersections that accompanies the out-of-plane displacement of the carbonylmore » group is observed in aqueous solution. Decay through this pathway is not observed in the gas phase simulations, and our analysis indicates that the hydrogen bonds with solvent water molecules play a key role in stabilizing the potential energies of thymine in this additional decay pathway.« less