Kinetics of HO2+HO2→H2O2+O2:: Implications for stratospheric H2O2 -: art. no. 1299

[1] The reaction HO2 + HO2 --> H2O2 + O-2 (1) has been studied at 100 Torr and 222 K to 295 K. Experiments employing photolysis of Cl-2/CH3OH/O-2/N-2 and F-2/H-2/O-2/N-2 gas mixtures to produce HO2 confirmed that methanol enhanced the observed reaction rate. At 100 Torr, zero methanol, k(1) = (8.8 +/- 0.9) 10(-13) x exp[(210 +/- 26)/T] cm(3) molecule(-1) s(-1) (2 uncertainties), which agrees with current recommendations at 295 K but is nearly 2 times slower at 231 K. The general expression for k(1), which includes the dependence on bath gas density, is k(1) = (1.5 +/- 0.2) x 10(-12) exp[(19 +/- 31)/T] + 1.7 x 10(-33) [M] x exp[1000/T], where the second term is taken from the JPL00-3 recommendation. The revised rate largely accounts for a discrepancy between modeled and measured [H2O2] in the lower to middle stratosphere.