Peeters Jozef, Nguyen Vinh Son, Müller Jean-François
Department of Chemistry, University of Leuven , B-3001 Heverlee, Belgium.
Belgian Institute for Space Aeronomy , Avenue Circulaire 3, B-1180 Brussels, Belgium.
J Phys Chem Lett. 2015 Oct 15;6(20):4005-11. doi: 10.1021/acs.jpclett.5b01787. Epub 2015 Sep 24.
The atmospheric oxidation of vinyl alcohol (VA) produced by photoisomerization of acetaldehyde (AA) is thought to be a source of formic acid (FA). Nevertheless, a recent theoretical study predicted a high rate coefficient k1(298 K) of ≈10(-14) cm(3) molecule(-1) s(-1) for the FA-catalyzed tautomerization reaction 1 of VA back into AA, which suggests that FA buffers its own production from VA. However, the unusually high frequency factor implied by that study prompted us to reinvestigate reaction 1 . On the basis of a high-level ab initio potential energy profile, we first established that transition state theory is applicable, and derived a k1(298 K) of only ≈2 × 10(-20) cm(3) molecule(-1) s(-1), concluding that the reaction is negligible. Instead, we propose and rationalize another important VA sink: its uptake by aqueous aerosol and cloud droplets followed by fast liquid-phase tautomerization to AA; global modeling puts the average lifetime by this sink at a few hours, similar to oxidation by OH.
乙醛（AA）光异构化产生的乙烯醇（VA）的大气氧化被认为是甲酸（FA）的一个来源。然而，最近的一项理论研究预测，对于FA催化的VA互变异构反应1（VA变回AA），速率系数k1(298 K)约为10^(-14) cm³·分子⁻¹·s⁻¹，这表明FA缓冲了其自身由VA产生的过程。然而，该研究中暗示的异常高的频率因子促使我们重新研究反应1。基于高水平的从头算势能面，我们首先确定过渡态理论适用，并得出k1(298 K)仅约为2×10^(-20) cm³·分子⁻¹·s⁻¹，得出该反应可忽略不计的结论。相反，我们提出并解释了另一个重要的VA汇：它被气溶胶和云滴吸收，随后快速液相互变异构为AA；全球模型显示，通过这个汇的平均寿命为几个小时，与被OH氧化的情况类似。
