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Overtone Induced Photochemistry of Small Organic Acids

In overtone initiated chemistry, visible or near-infrared (IR) photons excite the overtones in the OH vibrational stretching mode to chemically relevant energies.  Even though the overtone cross-section is expected to be low compared to electronic state cross-sections, these photochemical pathways may be important due to the larger number of solar photons in the visible and near-IR spectra region and the attenuation of UV light at low altitudes or high solar zenith angles.  The overtone induced decarboxylation of small organics is expected to produce larger oligomers from the small organic acids in the solution phase.  These larger molecules may partition more extensively to the surface in organic aerosols than their small organic acid precursors; where they will be more readily available for reactions with gas phase oxidants.  The two systems I have focused on are malonic acid and pyruvic acid.  These systems were chosen because theoretical results suggest that overtone excitation should provide enough energy to initiate the reaction and that the energy should be deposited in a way to allow progression along the reaction coordinate.  In these experiments I excited concentrated (~5 M) solutions of these molecules with visible and near IR light from a tungsten halogen lamp and I looked for the gas-phase formation of CO2 using FTIR.



Bruker FT-IR Spectrometer
- Tensor
- IFS 66v/S

Langmuir-Blodgett Trough