What is measured by hyper-Rayleigh scattering from a liquid?

Area of Science:

• Nonlinear Optics
• Molecular Spectroscopy
• Physical Chemistry

Background:

• Hyper-Rayleigh scattering (HRS) probes molecular hyperpolarizability.
• Understanding molecular interactions in liquids is crucial for chemical physics.
• Previous studies often neglect long-range correlations and ion-induced effects.

Purpose of the Study:

• To analyze polarization and angle dependence of HRS in acetonitrile and DMSO.
• To investigate contributions from random molecules, collisions, and ion fields.
• To determine long-range correlation functions using HRS and molecular dynamics.

Main Methods:

• Experimental measurement of HRS polarization and angle dependence.
• Analysis of contributions from molecular orientation, collisions, and ion fields.
• Integration with molecular dynamics simulations to determine correlation functions.

Main Results:

• Acetonitrile shows transverse HRS due to dipole-dipole interactions and long-range orientation correlation (r > 100 nm).
• Collision-induced HRS in acetonitrile indicates long-range intermolecular mode correlation.
• DMSO exhibits strong longitudinal HRS from collision-induced effects, with weak ion influence due to molecular geometry.

Conclusions:

• Both acetonitrile and DMSO display long-range correlations (r^-3) in molecular orientation and intermolecular modes.
• Ion-induced HRS is significant in acetonitrile but weak in DMSO.
• Collision-induced contributions are vital for understanding HRS in these liquids.