Markus Charles R, Winiberg Frank A F, Percival Carl J, Okumura Mitchio, Sander Stanley P
Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Dr, Pasadena, California 91011, United States.
Division of Chemistry and Chemical Engineering, California Institute of Technology, 1200 E. California Blvd, Pasadena, California 91125, United States.
J Phys Chem A. 2025 May 1;129(17):3807-3816. doi: 10.1021/acs.jpca.4c08240. Epub 2025 Apr 22.
The cross reaction between the free radicals OH and HO plays a critical role in a wide range of environments, including combustion and the atmospheres of Earth and Mars. In the middle atmosphere on Earth, it is the ultimate terminating step of odd-hydrogen chemistry, which has significant implications for the abundance of ozone. Recent laboratory measurements have brought established rate coefficients into question, introducing additional uncertainties into chemical models of the upper stratosphere and mesosphere. In this work, we present measurements of the rate coefficient from 265350 K using high-resolution infrared and ultraviolet kinetic spectroscopy. A scheme was developed which almost entirely avoids interfering reactions, providing a direct measurement of the decay of OH due to HO and reduces uncertainties associated with absolute calibration of OH and HO concentrations. We find a room temperature rate coefficient of (295) = (9.0 ± 1.9) × 10 cm molecule s (1σ error) and a slight temperature dependence over 265-330 K with an /R of -155 ± 50 K.
自由基OH和HO之间的交叉反应在包括燃烧以及地球和火星大气等广泛环境中起着关键作用。在地球的中层大气中，它是奇数氢化学的最终终止步骤，这对臭氧的丰度有重大影响。最近的实验室测量对已确定的速率系数提出了质疑，给平流层上部和中间层的化学模型带来了额外的不确定性。在这项工作中，我们使用高分辨率红外和紫外动力学光谱法给出了265 - 350 K温度范围内速率系数的测量结果。我们开发了一种几乎完全避免干扰反应的方案，直接测量了由于HO导致的OH衰减，并减少了与OH和HO浓度绝对校准相关的不确定性。我们发现室温下的速率系数k(295 K) = (9.0 ± 1.9)×10⁻¹² cm³ molecule⁻¹ s⁻¹(1σ误差)，并且在265 - 330 K范围内有轻微的温度依赖性，Eₐ/R为 - 155 ± 50 K。
