Carbonyl oxides as reactive intermediates in the lower atmosphere and the effect of optical excitation

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For several years carbonyl oxides ("Criegees") are established as important reactive intermediates in the lower atmosphere whose role - especially upon electronic excitation - is nevertheless not well understood. In the project the spectroscopy and photophysics of electronically excited carbonyl oxides are to be investigated theoretically by a combination of accurate electronic structure computations and multidimensional wavepacket propagations on coupled potential energy surfaces. Thereby ambiguous experimental results and conflicting interpretations of the UV spectra of even the smallest system CH2OO are to be clarified. In addition to the spectral intensity profile also the internal conversion dynamics of the relevant (mostly singlet) excited states is of interest. From the results of these and related studies a coherent picture of the dynamics of these carbonyl oxides after photoexcitation is expected to emerge, which should provide the basis of a better understanding of the photochemical elementary processes in the lower atmosphere (troposphere). To arrive at conclusive results, the project focusses - as already indicated above - on carbonyl oxides with up to three carbon atoms; for a number of years the latter species are also subject to intense experimental investigations.