9217584 Slanger The photochemistry of the earth's atmosphere is dominated by molecular oxygen in its diatomic and triatomic forms. Oxygen absorbs much of the solar radiation in the ultraviolet for 100 to 240 nm, leading to the formation of ozone. The structured nature of the oxygen absorption spectrum, and the consequent wide variations in the absorption cross section, mean that uv radiation is absorbed over a wide range of altitudes. Some wavelengths are absorbed above 100 km, while others descend below 40km, where they can initiate chemistry in anthropogenic species diffusing upward from the ground. Thus quantitative modeling of ozone production and other solar-induced photochemistry in the atmosphere requires detailed knowledge of the absorption spectrum of ozone, the spectral distribution of ultraviolet solar radiation (including solar cycle variations), and radiative transport through the atmosphere. Recent research in laborators and elsewhere suggests that the existing data and mechanistic understanding are far from adequate. This project involves experimental, theoretical, and modeling research to improve our knowledge of the absorption of ultraviolet radiation in the atmosphere. Four main topics are emphasized: (1) measurement of rotational and finestructure resolved linewidths for each upper vibrational level in the ozone Schumann-Runge band system; (2) theoretical analysis of the interactions between the ozone state and its four predissociating states, based on the experimental linewidths, (3) comparison of current models for solar energy deposition with that resulting from folding the experimental linewidths into the true solar spectrum; and (4) measurement of line-resolved absolute photoabsorption cross sections for ozone in the A-X,A'-X, and c-X Herzberg bands.
