RATE AND MECHANISM OF THE ATMOSPHERIC DEGRADATION OF 2H-HEPTAFLUOROPROPANE (HFC-227)

The atmospheric chemical behaviour of 2H-Heptafluoropropane (CF3CHFCF3 , HFC-227) with respect to its rate and mechanism of degradation in th e troposphere has been investigated. The rate coefficient for the reac tion of HFC-227 with OH radicals has been determined in direct time re solved experiments using a combination of laser-pulse initiation and L IF. In the temperature range T = 298-463 K the Arrhenius expression k( T) = (3.8+/-0.8)10(-13) exp(-1596+/-77 K/T) cm3/s, which corresponds t o k (298 K) = (1.8+/-0.3) 10(-15) CM3/s, was found. The mechanism of t he atmospheric degradation of HFC-227 has been investigated using both , laser-pulse initiated/time resolved and UV photolysis/FTIR product s tudies. It is concluded that the major carbonyl products are CF3COF an d CF2O which result from the decomposition of the oxy radical CF3CF(O) CF3 by C-C bond fission. The rate coefficient for this decomposition p rocess has been determined to be k = (2+/-1) 10(3) s-1 at 298 K. Based on the reactivity of HFC-227 with respect to the reaction with OH rad icals, the atmospheric lifetime and the GWP value for HFC-227 are esti mated to be approximately 40 years and 0.6+/-0.2, respectively.