title: Spectroscopic and kinetic properties of HO(2) radicals and the enhancement of the HO(2) self reaction by CH(3)OH and H(2)O.
abstract: The line center absorption cross sections and the rate constants for self-reaction of hydroperoxy radicals (HO(2)) have been examined in the temperature range of 253-323 K using pulsed laser photolysis combined with tunable diode laser absorption in the near-IR region. The transition probed was in the 2nu(1) OH overtone transition at 1506.43 nm. The temperature dependence of the rate constant (k) for the HO(2) + HO(2) reaction was measured relative to the recommended value at 296 K, giving k = (3.95 +/- 0.45) x 10(-13) x exp[(439 +/- 39)/T] cm(3) molecule(-1) s(-1) at a total pressure of 30 Torr (N(2) + O(2)). After normalizing our determination and previous studies at low pressure, we recommend k = (2.45 +/- 0.50) x 10(-13) x exp[(565 +/- 130)/T] cm(3) molecule(-1) s(-1) (0 < P < 30 Torr, 95% confidence limits). The observed rate coefficient, k(obs), increases linearly with CH(3)OH concentration, and the enhancement coefficient (k'), defined by k(obs) = k + k'[CH(3)OH], is found to be (3.90 +/- 1.87) x 10(-35) x exp[(3849 +/- 135)/T] cm(6) molecule(-2) s(-1) at 30 Torr. The analogous water vapor enhancement coefficient (k'') is (1.16 +/- 0.58) x 10(-36) x exp[(4614 +/- 145)/T] cm(6) molecule(-2) s(-1). The pressure-broadened HO(2) absorption cross section is independent of temperature in the range studied. The line center absorption cross sections at 1506.43 nm, after correction for instrumental broadening, are (4.3 +/- 1.1) x 10(-19), (2.8 +/- 0.7) x 10(-19), and (2.0 +/- 0.5) x 10(-19) cm(2)/molecule at total pressures of 0, 30, and 60 Torr, respectively (95% confidence limits).
authors.affiliation: Atmospheric Chemistry Division, National Center for Atmospheric Research, Boulder, Colorado 80307, USA.
authors.forename: Yongxin
authors.initials: Y
authors.lastname: Tang
authors.forename: Geoffrey S
authors.initials: GS
authors.lastname: Tyndall
authors.forename: John J
authors.initials: JJ
authors.lastname: Orlando