THE NEAR UV ABSORPTION-SPECTRA OF SEVERAL ALIPHATIC-ALDEHYDES AND KETONES AT 300-K

Absorption cross-sections are reported for acetaldehyde, propionaldehyde, isobutyraldehyde, n-butyraldehyde, acetone, 2-butanone, 2-pentanone, and 3-pentanone at wavelengths greater than 200 nm, a temperature of 300 K, and a spectral resolution of 0.50 nm. In general, the results are in good agreement with previous measurements of the spectra of these molecules, but are of higher precision than past measurements. For acetaldehyde, propionaldehyde, isobutyraldehyde, and acetone the cross-section results are combined with previous experimental measurements of the primary quantum yield for photolysis to estimate photodissociation rate constants for a representative set of atmospheric conditions. For the other four carbonyl compounds, upper limits for the photodissociation rate constant are calculated assuming a primary quantum yield of unity at all wavelengths. For acetaldehyde, photolysis is slow in comparison with reaction with hydroxyl radical. For the larger aldehydes and for acetone, photolysis and reaction with OH radical take place at comparable rates. For larger ketones, if the quantum yields for photolysis are unity, as assumed in our calculations, the rate of loss of the compounds by photodissociation could be important compared to reaction with hydroxyl radical.