Anisotropic X-Ray Scattering of Transiently Oriented Water

Area of Science:

• Physical Chemistry
• Materials Science
• Condensed Matter Physics

Background:

• Understanding the ultrafast structural dynamics of liquid water is crucial for many chemical and biological processes.
• Previous studies have explored water's response to external stimuli, but direct observation of transient structural changes remains challenging.

Purpose of the Study:

• To investigate the time-resolved structural dynamics of liquid water following optical excitation.
• To quantify transient changes in the oxygen-oxygen pair distribution function and molecular alignment.

Main Methods:

• Time-resolved anisotropic x-ray scattering under optical Kerr effect conditions.
• Polarizable molecular dynamics simulations.

Main Results:

• Anisotropic scattering decay of 160 fs was observed, distinct from a delayed temperature increase at 1 ps.
• Simulations successfully reproduced experimental results, showing transient molecular alignment along the electric field.
• Nearest-neighbor distances in water were found to shorten due to this alignment.
• Analysis revealed differing polarizabilities between two hypothesized fluctuating water configurations.

Conclusions:

• The study provides direct experimental evidence of ultrafast structural changes in liquid water induced by an optical field.
• Molecular alignment is identified as a key mechanism driving these transient structural modifications.
• The findings offer insights into the relationship between molecular polarizability and local structure in water.