Study of resonance Raman cross section of aqueous <Emphasis Type="BoldItalic">β</Emphasis> -carotene at low concentrations

Applying Teflon-AF waveguide cell, we determined the absolute resonance Raman cross sections (RCS) for C=C and C-C stretching modes of β-carotene in aqueous solution at low concentrations (10^-6–10^-10 M) by measuring Raman intensity. It was unexpected that the RCS increased rapidly with the decrease of concentration at extremely low concentration range (10^-8–10^-10 M), and it reached the value of 1.22×10^-21 cm² molecule^-1Sr^-1 at 2.5×10^-10 M larger than general RCS (10^-30 cm² molecule^-1Sr^-1) for 10⁹ times. Additionally, we give the tentative theory exploration for the experimental results that the large RCSs at low concentrations attributed to both resonance Raman effect and dipole-induced dipole interactions between solute and solvent molecules. PACS 33.20.Fb; 87.64.Je; 42.81.Wg