Kanno Nozomu, Tonokura Kenichi, Tezaki Atsumu, Koshi Mitsuo
Department of Chemical System Engineering, School of Engineering, The University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-8656, Japan.
J Phys Chem A. 2005 Apr 14;109(14):3153-8. doi: 10.1021/jp044592+.
Transient absorption spectra and decay profiles of HO2 have been measured using cw near-IR two-tone frequency modulation absorption spectroscopy at 297 K and 50 Torr in diluent of N2 in the presence of water. From the depletion of the HO2 absorption peak area following the addition of water, the equilibrium constant of the reaction HO2 + H2O <--> HO2-H2O was determined to be K2 = (5.2 +/- 3.2) x 10(-19) cm3 molecule(-1) at 297 K. Substituting K2 into the water dependence of the HO2 decay rate, the rate coefficient of the reaction HO2 + HO2-H2O was estimated to be (1.5 +/- 0.1) x 10(-11) cm3 molecule(-1) s(-1) at 297 K and 50 Torr with N2 as the diluent. This reaction is much faster than the HO2 self-reaction without water. It is suggested that the apparent rate of the HO2 self-reaction is enhanced by the formation of the HO2-H2O complex and its subsequent reaction. Results are discussed with respect to the kinetics and atmospheric chemistry of the HO2-H2O complex. At 297 K and 50% humidity, the concentration ratio of [HO2-H2O]/[HO2] was estimated from the value of K2 to be 0.19 +/- 0.11.
在297 K和50 Torr的氮气稀释剂中，于水存在的条件下，使用连续波近红外双音频率调制吸收光谱法测量了HO₂的瞬态吸收光谱和衰减曲线。通过添加水后HO₂吸收峰面积的减少，确定了反应HO₂ + H₂O <--> HO₂-H₂O在297 K时的平衡常数为K₂ = (5.2 ± 3.2)×10⁻¹⁹ cm³ molecule⁻¹。将K₂代入HO₂衰减速率对水的依赖性中，估计在297 K和50 Torr、以氮气为稀释剂的条件下，反应HO₂ + HO₂-H₂O的速率系数为(1.5 ± 0.1)×10⁻¹¹ cm³ molecule⁻¹ s⁻¹。该反应比无水时的HO₂自反应快得多。这表明HO₂自反应的表观速率因HO₂-H₂O络合物的形成及其后续反应而增强。针对HO₂-H₂O络合物的动力学和大气化学对结果进行了讨论。在297 K和50%湿度下，根据K₂的值估计[HO₂-H₂O]/[HO₂]的浓度比为0.19 ± 0.11。
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