“…Pyruvic acid is abundant in the atmosphere both in the gas phase and in aerosols as it is an oxidative product of isoprene. − Pyruvic acid has been used as a proxy for modeling the behavior of other atmospheric α-dicarbonyls. , Solutions of pyruvic acid have been used as a model for organic aerosol matter . Pyruvic acid can be decarboxylated with UV excitation, ,,− thermally, ,,,, and through infrared multiphoton pyrolysis. − Recent gas-phase experimental and theoretical results suggest that pyruvic acid should be the ideal model system to use for the experimental observation of the vibrational overtone initiated photochemical reaction of α-dicarbonyls. ,, In gas-phase pyruvic acid experiments, significant spectral broadening was observed for the excitation of the third (Δν OH = 4) and fourth (Δν OH = 5) overtone of the lowest energy conformer of pyruvic acid. ,, Theoretical results helped assign this broadening as being due the initiation of a concerted reaction of pyruvic acid, where two covalent bonds are broken simultaneously at energies below the bond dissociation energy. ,, The predicted photoproducts are CO 2 and methylhydroxycarbene. , However, due to the low density of pyruvic acid molecules in the gas phase and the low absorption cross sections of the overtones, the formation of CO 2 and other organic photoproducts were not experimentally observed.…”