Boakes Gavin, Hindy Mok W H, Rowley David M
Department of Chemistry, University College London, Christopher Ingold Laboratories, 20 Gordon Street, London, WC1H 0AJ, UK.
Phys Chem Chem Phys. 2005 Dec 21;7(24):4102-13. doi: 10.1039/b510308h. Epub 2005 Oct 18.
The kinetics of the association reaction of ClO radicals: ClO + ClO + M --> Cl2O2+ M (1), have been investigated as a function of temperature T between 206.0-298.0 K and pressure p between 25-760 Torr using flash photolysis with time-resolved UV absorption spectroscopy. ClO radicals were generated following the photolysis of Br2/Cl2O mixtures in nitrogen diluent gas. Charge coupled device (CCD) detection of time resolved absorptions was used to monitor ClO radicals over a broad wavelength window covering the ClO (A 2Pi<-- X 2Pi) vibronic absorption bands. The high pass filtered ClO absorption cross sections were calibrated as a function of temperature between T = 206.0-320 K, and exhibit a negative temperature dependence. The ClO association kinetics were found to be more rapid than those reported in previous studies, with limiting low and high pressure rate coefficients, in nitrogen bath gas, k0 = (2.78 +/- 0.82) x 10(-32) x (T/300)(-3.99 +/- 0.94) molecule(-2) cm6 s(-1) and k(infinity) = (3.37 +/- 1.67) x 10(-12) x (T/300)(-1.49 +/- 1.81) molecule(-1) cm3 s(-1), respectively, (obtained with the broadening factor F(c) fixed at 0.6). Errors are 2sigma. The pressure dependent ClO association rate coefficients (falloff curves) exhibited some discrepancies at low pressures, with higher than expected rate coefficients on the basis of extrapolation from high pressures (p > 100 Torr). Reanalysis of data excluding kinetic data recorded below p = 100 Torr gave k0 = (2.79 +/- 0.85) x 10(-32) x (T/300)(-3.78 +/- 0.98) molecule(-2) cm6 s(-1) and k(infinity) = (3.44 +/- 1.83)x 10(-12) x (T/300)(-1.73 +/- 1.91) molecule(-1) cm3 s(-1). Potential sources of the low pressure discrepancies are discussed. The expression for k(0) in air bath gas is k0 = (2.62 +/- 0.80) x 10(-32) x (T/300)(-3.78 +/- 0.98) molecule(-2) cm6 s(-1). These results support upward revision of the ClO association rate coefficient recommended for use in stratospheric models, and the stratospheric implications of the results reported here are briefly discussed.
利用闪光光解和时间分辨紫外吸收光谱，研究了ClO自由基缔合反应ClO + ClO + M --> Cl2O2 + M (1)的动力学，该反应是温度T在206.0 - 298.0 K以及压力p在25 - 760托之间的函数。在氮气稀释气体中，通过Br2/Cl2O混合物的光解产生ClO自由基。采用电荷耦合器件(CCD)对时间分辨吸收进行检测，以在覆盖ClO (A 2Pi<-- X 2Pi)振转吸收带的宽波长窗口内监测ClO自由基。高通滤波后的ClO吸收截面在T = 206.0 - 320 K之间作为温度的函数进行了校准，呈现出负温度依赖性。发现ClO缔合动力学比先前研究报道的更快，在氮气浴气中，极限低压和高压速率系数分别为k0 = (2.78 ± 0.82) x 10(-32) x (T/300)(-3.99 ± 0.94) 分子(-2) cm6 s(-1)和k(∞) = (3.37 ± 1.67) x 10(-12) x (T/300)(-1.49 ± 1.81) 分子(-1) cm3 s(-1)，(在展宽因子F(c)固定为0.6的情况下获得)。误差为2σ。压力依赖的ClO缔合速率系数(衰减曲线)在低压下存在一些差异，基于高压(p > 100托)外推得到的速率系数高于预期。对排除p = 100托以下记录的动力学数据后的数据重新分析，得到k0 = (2.79 ± 0.85) x 10(-32) x (T/300)(-3.78 ± 0.98) 分子(-2) cm6 s(-1)和k(∞) = (3.44 ± 1.83) x 10(-12) x (T/300)(-1.73 ± 1.91) 分子(-1) cm3 s(-1)。讨论了低压差异的潜在来源。在空气浴气中k(0)的表达式为k0 = (2.62 ± 0.80) x 10(-32) x (T/300)(-3.78 ± 0.98) 分子(-2) cm6 s(-1)。这些结果支持对用于平流层模型的ClO缔合速率系数进行向上修正，并简要讨论了此处报道结果对平流层的影响。
