澳大利亚新南威尔士大学Kable, Scott H.团队报道了HCHO光物理氧化产生HO₂自由基。相关研究成果于2023年7月6日发表在《自然—化学》。

甲醛（HCHO）是大气中体积最高的羰基。它吸收波长小于330nm的阳光，光解形成H和HCO自由基，然后与O₂反应形成HO₂。

该文中，研究人员展示了HCHO有一个额外的HO₂形成途径。当光解能量低于自由基形成的能量阈值时，研究人员通过腔衰荡光谱在低压下直接检测HO₂，并通过傅里叶变换红外光谱最终产物分析在1bar下间接检测HO₂。在电子结构理论和主方程模拟的支持下，研究人员将这种HO₂归因于光物理氧化（PPO）：光激发的HCHO非辐射地弛豫到基态，在基态，远离平衡的振动激活的HCHO分子与热O₂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会随着O₂压力的增加而增加。

附：英文原文

Title: Photophysical oxidation of HCHO produces HO2 radicals

Author: Welsh, Blair A., Corrigan, Maggie E., Assaf, Emmanuel, Nauta, Klaas, Sebastianelli, Paolo, Jordan, Meredith J. T., Fittschen, Christa, Kable, Scott H.

Issue&Volume: 2023-07-06

Abstract: Formaldehyde, HCHO, is the highest-volume carbonyl in the atmosphere. It absorbs sunlight at wavelengths shorter than 330nm and photolyses to form H and HCO radicals, which then react with O2 to form HO2. Here we show HCHO has an additional HO2 formation pathway. At photolysis energies below the energetic threshold for radical formation we directly detect HO2 at low pressures by cavity ring-down spectroscopy and indirectly detect HO2 at 1bar by Fourier-transform infrared spectroscopy end-product analysis. Supported by electronic structure theory and master equation simulations, we attribute this HO2 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 O2. PPO is likely to be a general mechanism in tropospheric chemistry and, unlike photolysis, PPO will increase with increasing O2 pressure.

DOI: 10.1038/s41557-023-01272-4

Source: https://www.nature.com/articles/s41557-023-01272-4