Reactions of Nitrate in Aqueous Droplets Initiated by Triplet Energy Transfer
PYEONGEUN KIM, Christian Boothby, Vicki Grassian, Robert Continetti,
University of California San Diego Abstract Number: 399
Working Group: Aerosol Chemistry
AbstractIn-situ Raman spectroscopy of single levitated aqueous microdroplets irradiated by dual-beam (266 and 532 nm) lasers demonstrates that nitrate anion 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, fast decrease of nitrate concentration was observed when SA is present in the droplet. This photo-induced reaction of nitrate occurs without the direct photolysis. Instead, the rate of nitrate depletion was found to be dependent on the initial concentration of SA and pH of the droplet. Based on the absorption-emission spectral analysis and time dependent density functional theory (TD-DFT) excited-state energy calculations, triplet-triplet energy transfer between SA and nitrate is proposed as the underlying mechanism for the enhanced depletion of nitrate in aqueous microdroplets. These results suggest that energy transfer mechanisms initiated by light-absorbing organic molecules may play a significant role in nitrate photochemistry.