Observation of Rayleigh optical activity for chiral molecules: a new chiroptical tool

TL;DR

The paper addresses the lack of experimental observation of Rayleigh optical activity (RayOA) in isotropic chiral samples and demonstrates a dedicated SCP-based RayOA instrument at $532\,\text{nm}$ to measure the circular intensity differential $Δ$ in Rayleigh scattering from neat α-pinene. Using off-resonance theory $Δ ≈ \frac{1}{c}\frac{24β(G′)^2-8β(A)^2}{12β^2}$ and quantum-chemical calculations across multiple functionals, the authors predict robust signs and magnitudes for $Δ$. They observe $Δ = ±3.6×10^{−4}$ for the two enantiomers, with measured signs matching predictions and absolute configuration, confirming RayOA as a practical chiroptical tool. This approach provides access to electric quadrupole information via isotropic samples and offers a potentially simpler, complementary route to absolute configuration determination compared with traditional methods like OR or CD, with implications for rapid chiroptical characterization and sensing.

Abstract

By measuring a small circularly polarized component in the scattered light, we report the first observation of Rayleigh optical activity (RayOA) for isotropic samples of chiral molecules, namely the two enantiomers of $α$-pinene in neat liquid form. Our work validates fundamental theoretical predictions made over fifty years ago and expands the chiroptical toolkit.

Figures (1)

• Figure 1: Measured (black data points) and predicted (colored data points connected by straight lines) values of the circular intensity differential $\Delta$ for the enantiomers of $\alpha$-pinene.