ATMOSPHERIC CHEMISTRY OF HFC-236CB - SPECTROKINETIC INVESTIGATION OF THE CF3CF2CFHO2 RADICAL, ITS REACTION WITH NO AND NO2, AND THE FATE OF THE CF3CF2CFHO RADICAL

A pulse radiolysis technique was used to study the UV absorption spectrum of CF3CF2CFHO2 radicals (at 250 nm sigma = (175 +/- 36) x 10(-20) cm(2) molecule(-1)). The observed bimolecular rate constant for the self reaction of CF3CF2CFHO2 radicals was k(13obs) = (5.2 +/- 1.4) x 10(-12) cm(3) molecule(-1) s(-1). Rate constants for reactions of CF3CF2CFHO2 radicals with NO and NO2 were k(3) > 8 x 10(-12) and k(4) = (6.3 +/- 0.7) x 10(-12) cm(3) molecule(-1) s(-1), respectively. Using a FTIR spectrometer/smog chamber technique it was shown that, under atmospheric conditions, reaction with O-2 and decomposition via C-C bond scission are competing loss mechanisms for CF3CF2CFHO radicals. A lower limit of 10(5) s(-1) was deduced for the rate of decomposition of CF3CF2CFHO radicals via C-C bond scission at 296 K in 1 bar of SF6 diluent. It is estimated that in the atmosphere approximately 98% of CF3CF2CFHO radicals will undergo decomposition into C2F5 radicals and HC(O)F and 2% will react with O-2 to give C2F5C(O)F. As part of this work relative rate methods were used to measure rate constants of(1.3 +/- 0.3) x 10(-12) and (1.5 +/- 0.3) x 10(-15) cm(3) molecule(-1) s(-1) for the reactions of CF3CF2CFH2 with F and Cl atoms, respectively.