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INVESTIGATION OF THE CORRELATION BETWEEN THE ENERGY OF THE HIGHESTOCCUPIED MOLECULAR ORBITAL (HOMO) AND THE LOGARITHM OF THE OH RATECONSTANT OF HYDROFLUOROCARBONS AND HYDROFLUOROETHERS
Citation:
Bartolotti, L. AND E. Edney. INVESTIGATION OF THE CORRELATION BETWEEN THE ENERGY OF THE HIGHESTOCCUPIED MOLECULAR ORBITAL (HOMO) AND THE LOGARITHM OF THE OH RATECONSTANT OF HYDROFLUOROCARBONS AND HYDROFLUOROETHERS. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/J-95/276.
Description:
A regression based model was developed to determine whether highest occupied molecular orbital (HOMO) energies, calculated using Kohn-Sham orbital density functional theory (DFT) could be used to estimate the OH rate constants of hydrofluorocarbons (HFCS) and hydrofluoroethers (HFEs), proposed substitutes for stratospheric O3 depleting chlorofluorcarbons. he goodness of fit of the DFT model was compared with a second regression model, derived using recently reported HOMO energies obtained from Hartree Fock theory (HFT). oth models were employed to predict OH rate constants for a number of HFCs and HFEs whose rate constants have not been measured, thus providing data on the types of chemical structures that may increase the OH reactivity of the substitute and hence decrease its contribution to global warming. he estimated percent standard errors in the OH rate constant HFT and DFT regression models were 72% and 78% respectively. he goodness of fits were such that the models can differentiate between two rate constants only when their ratio exceeds about a factor of four. odel results suggest that (1) only a limited number of HFEs will have OH rate constants that are more than an order of magnitude greater than the value for their corresponding HFCs and (2) the strategy of introducing an ether linkage into an HFC to dramatically enhance its reactivity will be most effective for the least fluorinated HFCS.