POTENTIAL CHLOROFLUOROCARBON REPLACEMENTS - OH REACTION-RATE CONSTANTS BETWEEN 250 AND 315-K AND INFRARED-ABSORPTION SPECTRA

We measured the rate constant for reactions of the OH radical with several potential chlorofluorocarbon replacements over the temperature range 251-314 K using laser photolysis laser-induced fluorescence techniques. The compounds studied and Arrhenius parameters determined from fits to the measured rate constants are as follows: CHF2OCHF2 (E 134), k(T) = (5.4 +/- 3.5) x 10(-13) cm3 s-1 exp [(-3.1 +/- 0.4 kcal mol-1)/RT]; CF3CH2CF3 (FC 236fa), k(T) = (2.0 +/- 1.0) X 10(-14) CM3 S-1 exp [(-1.8 +/- 0.3 kcal mol-1)/RT]; CF3CHFCH2F2 (FC 236ea), k(T) = (2.0 +/- 0.9) X 10(-13) CM3 S-1 exp [(-2.0 +/- 0.3 kcal mol-1)/RT]; and CF3CF2CH2F (FC 236cb), k(T) = (2.6 +/- 1.6) X 10(-13) cm3 S-1 exp [(-2.2 +/- 0.4 kcal mol-1)/RT]. The measured activation energies (2-3 kcal mol-1) are consistent with a mechanism of H atom abstraction. The tropospheric lifetimes, estimated from the measured OH reaction rates, and measured integrated infrared absorption cross sections over the range 770 to 1430 cm-1 suggest that E 134 and FC 236fa may have significant global warming potential. while FC 236ea and FC 236cb do not.