Pannacci Giacomo, Mancini Luca, Vanuzzo Gianmarco, Liang Pengxiao, Marchione Demian, Rosi Marzio, Casavecchia Piergiorgio, Balucani Nadia
Dipartimento di Chimica, Biologia e Biotecnologie, Università degli Studi di Perugia, Perugia, Italy.
Dipartimento di Ingegneria Civile e Ambientale, Università degli Studi di Perugia, Perugia, Italy.
Phys Chem Chem Phys. 2023 Aug 2;25(30):20194-20211. doi: 10.1039/d3cp01558k.
Acrylonitrile (CHCHCN) is ubiquitous in space (molecular clouds, solar-type star forming regions, and circumstellar envelopes) and is also abundant in the upper atmosphere of Titan. The reaction O(P) + CHCHCN can be of relevance in the chemistry of the interstellar medium because of the abundance of atomic oxygen. The oxidation of acrylonitrile is also important in combustion as the thermal decomposition of pyrrolic and pyridinic structures present in fuel-bound nitrogen generates many nitrogen-bearing compounds, including acrylonitrile. Despite its relevance, limited information exists on this reaction. We report a combined experimental and theoretical investigation of the reactions of acrylonitrile with both ground P and excited D atomic oxygen. From product angular and time-of-flight distributions in crossed molecular beam experiments with mass spectrometric detection at a collision energy, , of 31.4 kJ mol, we have identified the primary reaction products and determined their branching fractions (BFs). Theoretical calculations of the relevant triplet and singlet potential energy surfaces (PESs) were performed to interpret the experimental results and elucidate the reaction mechanism. Adiabatic statistical calculations of product BFs for the decomposition of the main triplet and singlet intermediates have been carried out. Combining the experimental and theoretical results, we conclude that the O(P) reaction leads to two main product channels: (i) CHCNH (ketenimine) + CO (dominant with a BF of 0.87 ± 0.05), formed efficient intersystem crossing from the entrance triplet PES to the underlying singlet PES, and (ii) HCOCHCN + H (minor, with a BF of 0.13 ± 0.05), occurring adiabatically on the triplet PES. Our study suggests the inclusion of this reaction as a possible destruction pathway of CHCHCN and a possible formation route of CHCNH in the interstellar medium. The O(D) + CHCHCN reaction mainly leads to the formation of CHCNH + CO adiabatically on the singlet PES. This result can improve models related to the chemistry of interstellar ice and cometary comas, where O(D) reactions can play a role. Overall, our results are expected to be useful for improving the models of combustion and extraterrestrial environments.
丙烯腈（CHCHCN）在太空中无处不在（分子云、太阳型恒星形成区域和星际包层），在土卫六的高层大气中也很丰富。由于原子氧的丰度，反应O(P) + CHCHCN可能与星际介质的化学过程相关。在燃烧过程中，丙烯腈的氧化也很重要，因为燃料中结合氮的吡咯和吡啶结构的热分解会产生许多含氮化合物，包括丙烯腈。尽管其具有相关性，但关于该反应的信息有限。我们报告了对丙烯腈与基态P和激发态D原子氧反应的实验和理论相结合的研究。通过在碰撞能量为31.4 kJ mol的交叉分子束实验中进行质谱检测得到的产物角度和飞行时间分布，我们确定了主要反应产物并确定了它们的分支比（BFs）。进行了相关三重态和单重态势能面（PESs）的理论计算，以解释实验结果并阐明反应机理。对主要三重态和单重态中间体分解的产物BFs进行了绝热统计计算。结合实验和理论结果，我们得出结论，O(P)反应导致两个主要产物通道：（i）CHCNH（乙烯亚胺）+ CO（占主导，BF为0.87 ± 0.05），通过从入口三重态PES到下层单重态PES的有效系间窜越形成，以及（ii）HCOCHCN + H（次要，BF为0.13 ± 0.05），在三重态PES上绝热发生。我们的研究表明，将该反应纳入可能是星际介质中CHCHCN的一种破坏途径以及CHCNH的一种可能形成途径。O(D) + CHCHCN反应主要在单重态PES上绝热地导致CHCNH + CO的形成。这一结果可以改进与星际冰和彗发化学相关的模型，其中O(D)反应可能起作用。总体而言，我们的结果有望有助于改进燃烧和地外环境模型。
