Atmospheric reactions in condensed media such as water droplets, organic aerosols, soot, and sea salt particles are now assumed to play significant roles in the troposphere. Reactions at surfaces have attracted special attention, in particular those occurring at the air-water interface of water droplets, since water is present in almost all the atmospheric condensed matter. Polycyclic aromatic hydrocarbons (PAHs) are of special interest because they are present in considerable amounts in the atmosphere and might pose health issues such as allergies and cancer. While the reactive fates of lighter PAHs such as naphthalene are governed by gas-phase reactions, heavier PAHs such as pyrene and benzo[a]pyrene adsorb to surfaces of atmospheric aerosols where they undergo complex oxidation and photolytic reactions. The nature of aerosol surfaces and the extent to which they determine the photochemistry of various PAHs are not well understood. Interaction with a solvent or surface may significantly alter the character of electronic states of adsorbed species. Hence, modeling the surface effects using a rigorous level of theory becomes vital.In this study, the photochemistry of a model PAH - anthracene is investigated. The ground and low-lying electronic excited states of anthracene are computed in the gas phase, condensed phase and at the air-water interface. EOM-CC and TD-DFT methods are used for description of the electronically excited states while the effective fragment potential (EFP) method is employed to model the solvent. Quantum mechanics (QM)/EFP methodology allows rigorous account of solvent and surface effects on the electronic spectroscopy of chromophores providing a valuable insight on photochemistry of PAHs in the atmosphere.

Investigation of photochemistry of PAHs at the air-water interface: QM/EFP study

246th National Meeting (2013)

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