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 σ = (175 ± 36) × 10-20 cm2 molecule-1). The observed bimolecular rate constant for the self reaction of CF3CF2CFHO2 radicals was k13obs = (5.2 ± 1.4) × 10-12 cm3 molecule-1 s-1. Rate constants for reactions of CF3CF2CFHO2 radicals with NO and NO2 were k3 > × 10-12 and k4 = (6.3 ± 0.7) × 10-12 cm3 molecule-1 s-1, respectively.

Using a FTIR spectrometer/smog chamber technique it was shown that, under atmospheric conditions, reaction with O2 and decomposition via C-C bond scission are competing loss mechanisms for CF3CF2CFHO radicals. A lower limit of 105 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 O2 to give C2F5C(O)F. As part of this work relative rate methods were used to measure rate constants of (1.3 ± 0.3) × 10-12 and (1.5 ± 0.3) × 10-15 cm3 molecule-1 s-1 for the reactions of CF3CF2CFH2 with F and Cl atoms, respectively.