Droplets provide unique opportunities for the investigation of laser-induced surface chemistry. Chemical reactions on the surface of charged droplets are ubiquitous in nature and can provide critical insight into more efficient processes for industrial chemical production. Here, we demonstrate the application of the reaction nanoscopy technique to strong-field ionized nanodroplets of propanediol (PDO). The technique’s sensitivity to the near-field around the droplet allows for the in-situ characterization of the average droplet size and charge. The use of ultrashort laser pulses enables control of the amount of surface charge by the laser intensity. Moreover, we demonstrate the surface chemical sensitivity of reaction nanoscopy by comparing droplets of the isomers 1,2-PDO and 1,3-PDO in their ion emission and fragmentation channels. Referencing the ion yields to gas-phase data, we find an enhanced production of methyl cations from droplets of the 1,2-PDO isomer. Density functional theory simulations support that this enhancement is due to the alignment of 1,2-PDO molecules on the surface. The results pave the way towards spatio-temporal observations of charge dynamics and surface reactions on droplets.

中文翻译：

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亚波长丙二醇液滴离子发射的反应纳米学

液滴为研究激光诱导的表面化学提供了独特的机会。带电液滴表面的化学反应在自然界中无处不在，可以为更有效的工业化学生产过程提供重要的洞察力。在这里，我们展示了反应纳米技术在丙二醇 (PDO) 的强场电离纳米液滴中的应用。该技术对液滴周围近场的敏感性允许对平均液滴尺寸和电荷进行原位表征。使用超短激光脉冲可以通过激光强度控制表面电荷量。此外，我们通过比较异构体 1,2-PDO 和 1,3-PDO 在其离子发射和碎裂通道中的液滴，证明了反应纳米显微镜的表面化学敏感性。参考气相数据的离子产率，我们发现 1,2-PDO 异构体的液滴产生的甲基阳离子增加了。密度泛函理论模拟支持这种增强是由于 1,2-PDO 分子在表面上的排列。该结果为液滴上电荷动力学和表面反应的时空观察铺平了道路。