Rate constants for the gas phase reactions of OH radicals with two isomers of tetrafluoropropene, CH(2)=CF-CF(3) (k(1)) and trans-CHF=CH-CF(3) (k(2)); were measured using a flash photolysis resonance-fluorescence technique over the temperature range 220 to 370 K. The Arrhenius plots were found to exhibit a noticeable curvature. The temperature dependences of the rate constants are very weak and can be represented by the following expressions over the indicated temperature intervals: k(1)(220-298 K) = 1.145 x 10(-12) x exp{13/T} cm(3) molecule(-1) s(-1), k(1)(298-370 K) = 4.06 x 10(-13) x (T/298)(1.17) x exp{+296/T} cm(3) molecule(-1) s(-1), k(2)(220-370 K) = 1.115 x 10(-13) x (T/298)(2.03) x exp{+522/T} cm(3) molecule(-1) s(-1). The overall accuracy of the rate constant measurements is estimated to be ca. 2% to 2.5% at the 95% confidence level. The uncertainty of the measured reaction rate constants is discussed in detail. The atmospheric lifetimes due to reactions with tropospheric OH were estimated to be 12 and 19 days respectively under the assumption of a well mixed atmosphere. IR absorption cross-sections were measured for both compounds and their global warming potentials were estimated.

The rate constant for the reaction of OH with HFC-245cb (CH 3 -CF 2 -CF 3 ) was measured by the flash photolysis resonance fluorescence technique over the temperature range 287-370 K in order to ascertain its atmospheric lifetime. Given the potential for trace levels of olefinic impurities to introduce errors into results of the rate constant measurements for low reactivity HFCs, considerable emphasis was placed on HFC purification and on demonstrating the utility of vacuum UV spectroscopy as a sensitive tool for detecting olefinic impurities in HFC samples. Measurements were also made of the OH rate constants for CH 2 dCH-CF 3 , CH 2 dCF-CF 3 , and CF 2 dCF-CF 3 , over the temperature range 252-370 K, and for CF 2 dCF 2 at 298 K. Absorption spectra for the four fluoroalkenes as well as for ethene and propene were obtained from 160 to 220 nm.

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Rate constants for the reactions of hydroxyl radicals with CH 3 CF 3 (HFC-143a) and CHF 2 CH 2 CF 3 (HFC245fa) have been measured using the flash photolysis resonance fluorescence technique over the temperature range 273-370 K. A data analysis procedure is presented which should minimize rate constant errors introduced by the possible effects of radical diffusion. The following Arrhenius expressions have been derived for the reactions of OH with CH 3 CF 3 and CHF 2 CH 2 CF 3 , respectively (in units of cm 3 molecule -1 s -1 ): (0.95 -0.17 +0.21 ) × 10 -12 exp{-(1979 ( 65)/T} and (0.632 -0.078 +0.089 ) × 10 -12 exp{-(1331 ( 43)/T}. With these values, the atmospheric lifetimes for the two HFCs have been estimated to be 51 and 7.4 years, respectively. An error analysis is presented from which the rate constant uncertainty at any temperature can be calculated.

The rate constant for the reaction of CH2ClBr with OH was measured by both flash photolysis resonance fluorescence and discharge flow electron paramagnetic resonance techniques over the temperature range 277−370 K. The Arrhenius expression × 10-12 exp{−(978 ± 72)/T} cm3 molecule-1 s-1 was derived from a composite fit to both data sets. Absorption cross-sections of CH2ClBr were measured from 187 to 290 nm at 295 K. The solubility of CH2ClBr in water was also estimated to determine if such a process could be important in determining the atmospheric lifetime of CH2ClBr. The atmospheric lifetime and ozone depletion potential for CH2ClBr were estimated.