Acidity-Dependent Atmospheric Organosulfate Structures and Spectra: Exploration of Protonation State Effects via Raman and Infrared Spectroscopies Combined with Density Functional Theory
Acidity-Dependent Atmospheric Organosulfate Structures and Spectra: Exploration of Protonation State Effects via Raman and Infrared Spectroscopies Combined with Density Functional Theory
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酸度依赖的大气有机硫酸盐结构和光谱：通过拉曼和红外光谱结合密度泛函理论探索质子化态效应
DOI：
10.1021/acs.jpca.2c04548
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发表时间：
2022
期刊：
影响因子：
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通讯作者：
Ault, Andrew P.
中科院分区：
文献类型：
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作者：
Fankhauser, Alison M.;Lei, Ziying;Daley, Kimberly R.;Xiao, Yao;Zhang, Zhenfa;Gold, Avram;Ault, Bruce S.;Surratt, Jason D.;Ault, Andrew P.
由有机衍生的氧化产物与硫酸根离子的非均相反应形成的有机硫酸盐可占二次有机气溶胶 (SOA) 质量的 15% 以上，主要是大气寿命较长的亚微米颗粒。然而，对有机硫酸盐分子结构的基本了解是有限的，特别是在与大气相关的酸度（pH = 0–6）下。在此，对于2-甲基四醇硫酸盐（2-MTS）这一重要的异戊二烯衍生有机硫酸盐，使用拉曼光谱和红外光谱以及中性（RO-SO3H）和阴离子/去质子化（RO-SO3-）结构的振动光谱的密度泛函理论（DFT）计算研究了质子化状态和振动模式。由于两种质子化状态的硫氧键顺序不同（中性和去质子化形式分别为 1 或 2 与 12/3），计算出的硫酸基振动有所不同。用拉曼实验仅观察到 1060 和 1041 cm-1 处的振动（与 2-MTS 阴离子的对称 S-O 伸缩相关），而没有观察到中性形式的硫酸根振动（~900、1200 和 1400 cm-1）。对其他 SOA 前体气体（α-蒎烯、β-石竹烯和甲苯）形成的有机硫酸盐的额外计算发现，RO-SO3- 在 1000 至 1100 cm-1 之间有类似的对称振动，与实验室实验中形成的相应有机硫酸盐一致。这些结果表明，有机硫酸盐主要在大气 pH 值下发生去质子化，这对气溶胶酸度、非均相反应和大气气溶胶中的持续化学有进一步的影响。
Organosulfates formed from heterogeneous reactions of organic-derived oxidation products with sulfate ions can account for >15% of secondary organic aerosol (SOA) mass, primarily in submicron particles with long atmospheric lifetimes. However, fundamental understanding of organosulfate molecular structures is limited, particularly at atmospherically relevant acidities (pH = 0–6). Herein, for 2-methyltetrol sulfates (2-MTSs), an important group of isoprene-derived organosulfates, protonation state and vibrational modes were studied using Raman and infrared spectroscopy, as well as density functional theory (DFT) calculations of vibrational spectra for neutral (RO–SO3H) and anionic/deprotonated (RO–SO3–) structures. The calculated sulfate group vibrations differ for the two protonation states due to their different sulfur–oxygen bond orders (1 or 2 versus 12/3for the neutral and deprotonated forms, respectively). Only vibrations at 1060 and 1041 cm–1, which are associated with symmetric S–O stretches of the 2-MTS anion, were observed experimentally with Raman, while sulfate group vibrations for the neutral form (∼900, 1200, and 1400 cm–1) were not observed. Additional calculations of organosulfates formed from other SOA-precursor gases (α-pinene, β-caryophyllene, and toluene) identified similar symmetric vibrations between 1000 and 1100 cm–1for RO–SO3–, consistent with corresponding organosulfates formed during laboratory experiments. These results suggest that organosulfates are primarily deprotonated at atmospheric pH values, which have further implications for aerosol acidity, heterogeneous reactions, and continuing chemistry in atmospheric aerosols.