Ultraviolet-visible-near-infrared absorption cross-sections of liquid oleic acid: contributions of overtone vibrations and impurities.

Authors

Shota Saito, Raiki Nishizawa, Naoki Numadate, Shinichi Enami, Hirokazu Kobayashi, Tetsuya Hama

Published in

Physical chemistry chemical physics : PCCP. Aug 21, 2026. Epub Aug 21, 2026.

Abstract

Unsaturated fatty acids such as liquid oleic acid (OA) have a significant role in atmospheric aerosol chemistry, and their photochemical processes have attracted increasing attention. However, the accurate determination of their ultraviolet-visible-near-infrared (UV-Vis-NIR) absorption cross-sections has been hindered by trace impurities present in commercial reagents. In this study, we developed a recrystallisation system to purify liquid OA and measured its UV-Vis-NIR absorption spectra over a wide wavelength range of 190-900 nm. We show that trace impurities (at most 0.3%) that are inherently present in commercial OA reagents dominate the absorbance at wavelengths of 270-400-nm. By successfully removing these impurities, we quantitatively obtained the upper limit of absorption cross-sections of neat liquid OA. We observed extremely weak absorption features in the Vis to NIR region, such as peaks near 650, 761, and 830 nm. These features were assigned to the fourth (Δν = 5) and fifth (Δν = 6) overtones of C-H stretching vibrations from methyl and methylene groups. Our findings highlight the need for careful purification in photochemical experiments and provide data for quantitatively understanding the sunlight-induced photochemistry of atmospheric organic aerosols.

PMID:
42626990
Bibliographic data and abstract were imported from PubMed on 21 Aug 2026.

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