Bourgalais Jérémy, Carrasco Nathalie, Vettier Ludovic, Gautier Thomas, Blanchet Valérie, Petit Stéphane, Descamps Dominique, Fedorov Nikita, Delos Romain, Gaudin Jérôme
LATMOS-IPSL, Université Versailles St-Quentin, CNRS/INSU, Sorbonne Université, UPMC Univ. Paris 06, 11 boulevard d'Alembert, 78280, Guyancourt, France.
CELIA, Université de Bordeaux - CNRS - CEA, UMR5107, 351 Cours de la Libération, F33405, Talence, France.
Sci Rep. 2020 Jun 19;10(1):10009. doi: 10.1038/s41598-020-66950-6.
The in situ exploration of Titan's atmosphere requires the development of laboratory experiments to understand the molecular growth pathways initiated by photochemistry in the upper layers of the atmosphere. Key species and dominant reaction pathways are used to feed chemical network models that reproduce the chemical and physical processes of this complex environment. Energetic UV photons initiate highly efficient chemistry by forming reactive species in the ionospheres of the satellite. We present here a laboratory experiment based on a new closed and removable photoreactor coupled here to an Extreme Ultraviolet (EUV) irradiation beam produced by the high-order harmonic generation of a femtosecond laser. This type of EUV stable source allow long-term irradiation experiments in which a plethora of individual reactions can take place. In order to demonstrate the validity of our approach, we irradiated for 7 hours at 89.2 nm, a gas mixture based on N/CH (5%). Using only one wavelength, products of the reaction reveal an efficient photochemistry with the formation of large hydrocarbons but especially organic compounds rich in nitrogen similar to Titan. Among these nitrogen compounds, new species had never before been identified in the mass spectra obtained in situ in Titan's atmosphere. Their production in this experiment, on the opposite, corroborates previous experimental measurements in the literature on the chemical composition of aerosol analogues produced in the laboratory. Diazo-compounds such as dimethyldiazene (CHN), have been observed and are consistent with the large nitrogen incorporation observed by the aerosols collector pyrolysis instrument of the Huygens probe. This work represents an important step forward in the use of a closed cell chamber irradiated by the innovative EUV source for the generation of photochemical analogues of Titan aerosols. This approach allows to better constrain and understand the growth pathways of nitrogen incorporation into organic aerosols in Titan's atmosphere.
对泰坦大气进行原位探测需要开展实验室实验，以了解大气上层光化学引发的分子生长路径。关键物种和主要反应路径被用于构建化学网络模型，该模型可再现这一复杂环境中的化学和物理过程。高能紫外光子通过在卫星电离层中形成活性物种引发高效化学反应。我们在此展示一项基于新型封闭且可移动光反应器的实验室实验，该光反应器与飞秒激光高次谐波产生的极紫外（EUV）辐照光束耦合。这种类型的EUV稳定光源可进行长期辐照实验，在此过程中会发生大量单独的反应。为证明我们方法的有效性，我们在89.2纳米波长下对基于N/CH（5%）的气体混合物辐照了7小时。仅使用一个波长，反应产物显示出高效的光化学过程，形成了大量碳氢化合物，尤其是富含氮的有机化合物，类似于泰坦大气中的情况。在这些含氮化合物中，有一些新物种在泰坦大气原位质谱中从未被识别过。相反，它们在本实验中的产生证实了文献中先前关于实验室中产生的气溶胶类似物化学成分的实验测量结果。已观察到重氮化合物，如二甲基重氮烯（CHN），这与惠更斯探测器的气溶胶收集器热解仪器所观察到的大量氮掺入情况一致。这项工作代表了在使用由创新EUV光源辐照的封闭腔室来生成泰坦气溶胶光化学类似物方面向前迈出的重要一步。这种方法有助于更好地限制和理解泰坦大气中氮掺入有机气溶胶的生长路径。
