Water structure, dynamics, and vibrational spectroscopy in sodium bromide solutions

Area of Science:

• Physical Chemistry
• Theoretical Spectroscopy
• Computational Chemistry

Background:

• Aqueous solutions with ions exhibit complex molecular behavior.
• Understanding ion-water interactions is crucial for various chemical and biological processes.
• The Hofmeister series describes ion-specific effects on protein solubility and water structure.

Purpose of the Study:

• To theoretically investigate the effects of sodium bromide on the vibrational spectroscopy of HOD in water.
• To develop new spectroscopic maps based on electronic-structure calculations.
• To understand the molecular-level mechanisms behind observed spectroscopic changes with varying salt concentrations.

Main Methods:

• Electronic-structure calculations on water-ion clusters.
• Development of new spectroscopic maps.
• Calculation of OD-stretch absorption line shapes and frequency time-correlation functions.

Main Results:

• Calculated OD-stretch absorption line shapes agree well with experimental data.
• Provided molecular insights into the concentration-dependent blueshift and nonmonotonic line width.
• Observed a 3-4 fold slowdown in spectral diffusion at high salt concentrations, attributed to anionic solvation shell rearrangements.
• Identified complex spectral diffusion processes occurring on multiple time scales beyond experimental reach.

Conclusions:

• The Hofmeister series likely reflects only local ordering of water molecules.
• Anionic solvation shell rearrangements play a significant role in relaxation dynamics.
• Theoretical spectroscopy provides valuable insights into ion-aqueous solution interactions.