Sea surface microlayer and sea spray aerosols are enriched with many light absorbing organic species. The systems are very complex and a wide range of reactions and photochemical reactions occur simultaneously. In order to better understand photochemical reactions in this complex environment, model systems are needed. Pyruvic acid is an important chemical compound involved in many metabolic pathways in cells of living organisms and also serves as a model system for α-dicarbonyls. Four different species of pyruvic acid are known to exist in water solution. Presented here is a combined experimental and theoretical study of the mechanism behind the photoabsorption spectrum of pyruvic acid and the influence of parameters such as pH and ionic strength. The theoretical part of the work is directed towards establishing the molecular mechanism of the photoabsorption spectrum. Theoretical spectra were obtained using two different approaches: (1) Calculation of vertical excitation energies using the ADC(2) method and (2) Molecular dynamics simulations using MP2 ground state potentials followed by calculations of vertical excitation energy on selected structures from the simulation. Different theoretical models were used for the simulation of the spectrum. The absorption spectra for each individual isolated species of pyruvic acid were not sufficient for explaining the main features of the experimental spectra. Therefore a water cluster environment with and without H3O+ was used as a model system for the experimental spectra. Ionic strengths were modeled by explicitly adding particular ions to the cluster. The theoretical calculations carried out for small finite clusters yield a good agreement with the experimental data and provide a microscopic picture of the steps and the interactions involved in the photoabsorption. Insights to the experimental spectrum obtained from this theoretical approach will be discussed.

Photochemical reaction dynamics and absorption spectroscopy of environmentally important species

2019 Fall National Meeting

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