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Robert W. Carr, Associate Fellow

Atmospheric Chemistry of the Chlorine-Containing Organic Compounds

This project is complementing experimental research on atmospheric chemistry of CH2ClO and CFCl2CH2O radicals. The rate coefficients of the reactions of CH2ClO radical with O2, NO, and the unimolecular elimination of HCl from the CH2ClO have been investigated experimentally by these researchers. Ab initio molecular orbital calculations have been done to predict the geometries and energies of the reactant, transition state, and products of the unimolecular elimination of HCl. Ab initio calculations are now being done on the reactions of CH2ClO with O2 and NO, and these are being compared with the experimental results. If successful, the ab initio calculations will also be done on the reactions of CFCl2CH2O with O2 and NO, and a comparison will be made between the computations and the experimental results. Comparison of estimated and experimental rate coefficients permit development of rate coefficient models accurate over the entire range of atmospheric conditions, which is much wider than the range of conditions accessible by experimental methods.

Man-made and naturally occuring chlorine-containing organic compounds are the source of the atomic chlorine that initiates reaction cycles causing ozone depletion. Methyl chloride is the most prevalent halocarbon in the atmosphere, and the CH2ClO radical is an intermediate in the oxidation of CH3Cl.

The rate coefficients of the reactions of CH2ClO radical with O2 and NO, and the unimolecular elimination of HCl from the CH2ClO were experimentally determined using ultraviolet flash photolysis with time-resolved mass spectrometry in the laboratory. Ab initio molecular orbital computations and RRKM calculations using models based on the ab initio results were also done to predict temperature and pressure dependence on the rate coefficients of the unimolecular elimination of HCl from the CH2ClO radical. The theoretical studies agree well with the experimental results.

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In order to better understand the reactivity of the CH2ClO radical, ab initio calculations are being done on the reactions of CH2ClO with O2 and NO, and the calculations are being compared with experimental results.

The gaussian series of programs are used to characterize reactants and products, to locate and characterize transition states, and to evaluate reaction paths. Ab initio calculations have been completed on unimolecular elimination of HCl from CH2ClO radical using an SGI workstation. Since the transition states of some reactions are much larger, supercomputing resources are required for these larger calculations. These calculational results will provide deeper insight into the reactivity of these oxy radicals than could be obtained by experiments alone. This will also give accurate representatives of these reactions over a wide range of temperature and pressure for use in atmospheric models.

This information is available in alternative formats upon request by individuals with disabilities. Please send email to alt-format@msi.umn.edu or call 612-624-0528.

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