Near Infrared Photochemistry of Pyruvic Acid in Aqueous Solution

Recent experimental and theoretical results have suggested that organic acids such as pyruvic acid, can be photolyzed in the ground electronic state by the excitation of the OH stretch vibrational overtone. These overtones absorb in the near-infrared and visible regions of the spectrum where the solar photons are plentiful and could provide a reaction pathway for the organic acids and alcohols that are abundant in the earth's atmosphere. In this paper the overtone initiated photochemistry of aqueous pyruvic acid is investigated by monitoring the evolution of carbon dioxide. In these experiments CO2 is being produced by excitation in the near-infrared, between 850 nm and similar to 1150 nm (11 765-8696 cm(-1)), where the second OH vibrational overtone (Delta v = 3) of pyruvic acid is expected to absorb. These findings show not only that the overtone initiated photochemical decarboxylation reaction occurs but also that in the aqueous phase it occurs at a lower energy than was predicted for the overtone initiated reaction of pyruvic acid in the gas phase (13 380 cm(-1)). A quantum yield of (3.5 +/- 1.0) X 10(-4) is estimated, suggesting that although this process does occur, it does so with a very low efficiency.