Abstract We report the photodegradation of optically trapped oleic acid droplets by visible light in the absence of additional reactive gaseous species. The temporal evolution of the droplet's chemical composition and size is monitored by Raman spectroscopy and elastic light scattering, respectively. The dependencies on the oxygen amount in the surrounding gas phase (~0–20%), the droplet size (~500–3000 nm in radius), and the laser power and wavelength are investigated. The oxygen amount and the droplet size have only a very minor influence on the reaction rate, if at all. By contrast, the reaction becomes substantially faster at higher laser power and shorter wavelength. The experimental observations indicate that mechanisms involving the photoexcitation of oleic acid are the dominant pathways. Our study reveals that direct photodegradation has to be accounted for when using optical traps or applying spectroscopic and light scattering characterization methods to study aerosol particles that contain fatty acids.

中文翻译：

---

单个光学捕获的油酸液滴的光化学

摘要 我们报告了在没有额外反应性气体物质的情况下，可见光对光学捕获的油酸液滴的光降解。液滴的化学成分和尺寸的时间演变分别由拉曼光谱和弹性光散射监测。研究了周围气相中氧含量（~0-20%）、液滴尺寸（半径~500-3000 nm）以及激光功率和波长的依赖性。氧气量和液滴尺寸对反应速率的影响很小，如果有的话。相比之下，反应在更高的激光功率和更短的波长下变得明显更快。实验观察表明，涉及油酸光激发的机制是主要途径。