Thermodynamics of oligomer formation: implications for secondary organic aerosol formation and reactivity
Thermodynamics of oligomer formation: implications for secondary organic aerosol formation and reactivity
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DOI：
10.1039/c3cp44586k
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发表时间：
2013-01-01
影响因子：
3.3
通讯作者：
Johnston, Murray V.
中科院分区：
文献类型：
--
作者：
DePalma, Joseph W.;Horan, Andrew J.;Johnston, Murray V.
二聚体和高阶低聚物，无论是气相还是颗粒相，都可以影响重要的大气过程，如新粒子的形成和气相颗粒的分配。本研究采用蒙特卡罗配置采样、半经验和密度泛函理论（DFT）量子力学以及连续介质溶剂模型相结合的方法，研究了a-蒎烯臭氧分解的各种氧化产物形成二聚体的热力学。在气相和凝聚相中均存在有利的二聚体形成途径。二聚体形成的自由能用于计算平衡常数和在各种条件下的预期二聚体浓度。在气相中，研究的有利途径包括形成非共价的萜烯酸和/或顺式蒎酸二聚体和共价结合的过氧半缩醛。在与大气相关的条件下，只有足够数量的萜烯酸才能形成二聚体，以促进新粒子的形成。在实验室实验中通常使用的条件下，几种二聚体的形成途径可能有助于颗粒的形成。在缩合相中，有利于形成萜烯酸和/或顺式蒎酸的非共价二聚体和代表过氧半缩醛和水合醛的共价结合二聚体。二聚体的形成取决于溶液和温度。类水溶液似乎比甲醇或乙腈溶液更能促进二聚体的形成。从298 K加热到373 K会导致大量分解回单体。在气相或缩合相中都不利于形成的二聚体包括半缩醛、酯、酸酐和二（α -羟基）醚。
Dimers and higher order oligomers, whether in the gas or particle phase, can affect important atmospheric processes such as new particle formation, and gas-particle partitioning. In this study, the thermodynamics of dimer formation from various oxidation products of a-pinene ozonolysis are investigated using a combination of Monte Carlo configuration sampling, semi-empirical and density functional theory (DFT) quantum mechanics, and continuum solvent modeling. Favorable dimer formation pathways are found to exist in both gas and condensed phases. The free energies of dimer formation are used to calculate equilibrium constants and expected dimer concentrations under a variety of conditions. In the gas phase, favorable pathways studied include formation of non-covalent dimers of terpenylic acid and/or cis-pinic acid and a covalently-bound peroxyhemiacetal. Under atmospherically relevant conditions, only terpenylic acid forms a dimer in sufficient quantities to contribute to new particle formation. Under conditions typically used in laboratory experiments, several dimer formation pathways may contribute to particle formation. In the condensed phase, non-covalent dimers of terpenylic acid and/or cis-pinic acid and covalently-bound dimers representing a peroxyhemiacetal and a hydrated aldol are favorably formed. Dimer formation is both solution and temperature dependent. A water-like solution appears to promote dimer formation over methanol-or acetonitrile-like solutions. Heating from 298 K to 373 K causes extensive decomposition back to monomers. Dimers that are not favorably formed in either the gas or condensed phase include hemi-acetal, ester, anhydride, and the di(alpha-hydroxy) ether.