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Published on: December 27, 2018
Photoinduced Reactions of Nitrate in Aqueous Microdroplets by Triplet Energy Transfer
Pyeongeun Kim1, Christian Boothby1, Vicki H Grassian1
1Department of Chemistry and Biochemistry, University of California San Diego, 9500 Gilman Drive, La Jolla, California, 92093-0340, United States.
Abstract:
In-situ Raman spectroscopy of single levitated charged aqueous microdroplets irradiated by dual-beam (266 and 532 nm) lasers demonstrates that the nitrate anion (NO3-) can be depleted in the droplet through an energy transfer mechanism following excitation of sulfanilic acid (SA), a UV-absorbing aromatic organic compound. Upon 266 nm irradiation, a fast decrease of the NO3- concentration was observed when SA is present in the droplet. This photoinduced reaction occurs without the direct photolysis of NO3-. Instead, the rate of NO3- depletion was found to depend on the initial concentration of SA and the pH of the droplet. Based on absorption-emission spectral analysis and excited-state energy calculations, triplet-triplet energy transfer between SA and NO3- is proposed as the underlying mechanism for the depletion of NO3- in aqueous microdroplets. These results suggest that energy transfer mechanisms initiated by light-absorbing organic molecules may play a significant role in NO3- photochemistry.
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