Photophysical oxidation of HCHO produces HO_2 radicals
Photophysical oxidation of HCHO produces HO_2 radicals
复制标题
HCHO的光物理氧化产生HO_2自由基
DOI：
10.1038/s41557-023-01272-4
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发表时间：
2023
期刊：
影响因子：
21.8
通讯作者：
S. Kable
中科院分区：
文献类型：
--
作者：
Blair A Welsh;M. E. Corrigan;E. Assaf;K. Nauta;P. Sebastianelli;M. J. Jordan;C. Fittschen;S. Kable
在大气中，甲醛的光解产生H和HCO自由基，然后与O_2反应生成HO_2（在将大气中的碳转化为CO_2中很重要）。现在已经表明，内激发态甲醛也能与大气中的O_2直接一步反应生成HO_2，这种反应机理在对流层中很可能是普遍的。甲醛是大气中含量最高的羰基化合物。它吸收波长小于330 nm的太阳光，光解生成H和HCO自由基，然后与O_2反应生成HO_2。在这里，我们表明HCHO有一个额外的HO_2形成途径。在光解能量低于自由基形成的能量阈值时，我们用光腔衰荡光谱直接检测低压下的HO_2，用傅里叶变换红外光谱终产物分析间接检测1 bar下的HO_2。在电子结构理论和主方程模拟的支持下，我们将这种HO_2归因于光物理氧化（PPO）：光激发的HCHO非辐射弛豫到基态电子态，在那里远离平衡的振动激活的HCHO分子与热O_2反应。PPO可能是对流层化学中的一种普遍机制，与光解不同，PPO将随O_2压力的增加而增加。
In the atmosphere, photolysis of formaldehyde generates H and HCO radicals, which then react with O_2 to form HO_2 (important in converting atmospheric carbon to CO_2). Now it has been shown that internally excited formaldehyde can also react with atmospheric O_2 to make HO_2 in a direct, one-step ‘photophysical oxidation’, a mechanism likely to be general in the troposphere. Formaldehyde, HCHO, is the highest-volume carbonyl in the atmosphere. It absorbs sunlight at wavelengths shorter than 330 nm and photolyses to form H and HCO radicals, which then react with O_2 to form HO_2. Here we show HCHO has an additional HO_2 formation pathway. At photolysis energies below the energetic threshold for radical formation we directly detect HO_2 at low pressures by cavity ring-down spectroscopy and indirectly detect HO_2 at 1 bar by Fourier-transform infrared spectroscopy end-product analysis. Supported by electronic structure theory and master equation simulations, we attribute this HO_2 to photophysical oxidation (PPO): photoexcited HCHO relaxes non-radiatively to the ground electronic state where the far-from-equilibrium, vibrationally activated HCHO molecules react with thermal O_2. PPO is likely to be a general mechanism in tropospheric chemistry and, unlike photolysis, PPO will increase with increasing O_2 pressure.