Prlj Antonio, Marsili Emanuele, Hutton Lewis, Hollas Daniel, Shchepanovska Darya, Glowacki David R, Slavíček Petr, Curchod Basile F E
Department of Chemistry, Durham University, Durham DH1 3LE, U.K.
Department of Physical Chemistry, University of Chemistry and Technology, Prague, Technická 5, Prague 16628, Czech Republic.
ACS Earth Space Chem. 2022 Jan 20;6(1):207-217. doi: 10.1021/acsearthspacechem.1c00355. Epub 2021 Dec 17.
Characterizing the photochemical reactivity of transient volatile organic compounds (VOCs) in our atmosphere begins with a proper understanding of their abilities to absorb sunlight. Unfortunately, the photoabsorption cross-sections for a large number of transient VOCs remain unavailable experimentally due to their short lifetime or high reactivity. While structure-activity relationships (SARs) have been successfully employed to estimate the unknown photoabsorption cross-sections of VOCs, computational photochemistry offers another promising strategy to predict not only the vertical electronic transitions of a given molecule but also the width and shape of the bands forming its absorption spectrum. In this work, we focus on the use of the nuclear ensemble approach (NEA) to determine the photoabsorption cross-section of four exemplary VOCs, namely, acrolein, methylhydroperoxide, 2-hydroperoxy-propanal, and (microsolvated) pyruvic acid. More specifically, we analyze the influence that different strategies for sampling the ground-state nuclear density-Wigner sampling and ab initio molecular dynamics with a quantum thermostat-can have on the simulated absorption spectra. We highlight the potential shortcomings of using uncoupled harmonic modes within Wigner sampling of nuclear density to describe flexible or microsolvated VOCs and some limitations of SARs for multichromophoric VOCs. Our results suggest that the NEA could constitute a powerful tool for the atmospheric community to predict the photoabsorption cross-section for transient VOCs.
要了解大气中瞬态挥发性有机化合物（VOCs）的光化学反应活性，首先要正确认识它们吸收太阳光的能力。不幸的是，由于大量瞬态VOCs寿命短或反应活性高，其实验光吸收截面尚无法获得。虽然结构-活性关系（SARs）已成功用于估算VOCs未知的光吸收截面，但计算光化学提供了另一种有前景的策略，不仅可以预测给定分子的垂直电子跃迁，还能预测形成其吸收光谱的谱带宽度和形状。在这项工作中，我们专注于使用核系综方法（NEA）来确定四种典型VOCs的光吸收截面，即丙烯醛、甲基过氧化氢、2-氢过氧丙醛和（微溶剂化的）丙酮酸。更具体地说，我们分析了不同的基态核密度采样策略——维格纳采样以及使用量子恒温器的从头算分子动力学——对模拟吸收光谱可能产生的影响。我们强调了在核密度的维格纳采样中使用非耦合谐波模式来描述柔性或微溶剂化VOCs的潜在缺点，以及SARs对多发色团VOCs的一些局限性。我们的结果表明，NEA可能成为大气科学界预测瞬态VOCs光吸收截面的有力工具。
