Kinetics of the reactions of the CHBr2 and CHBr2O2 radicals with O2 and NO.
When bromoform (CHBr3) is photolyzed at 266 or 303 nm in the presence of O2 and NO, the formation of secondary Br atoms is observed. By following the rate of growth of this secondary Br atom signal as a function of conditions, rate constants have been determined for the reactions CHBr2 + O2, CHBr2 + NO (both pressure-dependent), and CHBr2O2 + NO (k(2a) = (1.74 +/- 0.16) x 10(-11) cm3 molecule(-1) s(-1) at 23 degrees C). By measuring the amplitude of the secondary Br signal compared to the primary Br formed in the initial photolysis, it is established that the CHBr2O radical spontaneously decomposes to form CHBrO + Br at least 90%, and probably 100%, of the time, in agreement with previous work and with recent ab initio calculations. A survey of four other polybrominated methanes, CH2Br2, CHClBr2, CF2Br2, and CBr4, shows that they all generate secondary Br atoms when photolyzed at 266 nm in the presence of O2 and NO, suggesting that their reaction sequences are similar to that of bromoform.
Bayes
Kyle D
KD
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109, USA. kdbayes@jpl.nasa.gov
Friedl
Randall R
RR
Sander
Stanley P
SP
D005609:Free Radicals / Q000737:chemistry; D007700:Kinetics; D009569:Nitric Oxide / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry*; D022882:Trihalomethanes / Q000737:chemistry*
D005609:Free Radicals; D022882:Trihalomethanes; D009569:Nitric Oxide; D010100:Oxygen