ATMOSPHERIC CHEMISTRY OF CH2BRCL - KINETICS AND MECHANISM OF THE REACTION OF F-ATOM WITH CH2BRCL AND FATE OF THE CHBRCLO-CENTER-DOT RADICAL

The reaction of F atoms with CH2BrCl was studied using a pulsed radiol ysis technique and found to proceed via two channels: direct hydrogen abstraction and adduct formation. The adduct exists in equilibrium wit h F atoms and CH2BrCl. The equilibrium constant K-4 = [Adduct]/([CH2Br Cl][F]) (4.2 +/- 1.0) x 10(-16) cm(3)molecule(-1). In 1000 mbar total pressure of SF6 at 294 +/- 2 K, the yield of the adduct is 68 +/- 11% and the overall rate constant for reaction of F atoms with CH2BrCl is k(4) (1000 mbar) = (3.6 +/- 0.9) x 10(-11) cm(3) molecule(-1) s(-1). T he adduct reacts with NO with a rate constant of (2.09 +/- 0.41) x 10( -11) cm(3) molecule(-1) s(-1). The atmospheric fate of the alkoxy radi cal CHBrClO is Br atom elimination, which occurs at a rate estimated t o be >2 x 10(6) s(-1) in 700 Torr of air at 295 K. Relative rate techn iques were used to measure k(Cl + CH2BrCl) = (4.2 +/- 0.5) x 10(-13) a nd k(F + CH2BrCl --> CHBrCl + HF) = (1.2 +/- 0.4) x 10(-11) cm(3) mole cule(-1) s(-1). These results are compared to the available literature data.