CRC: Chemistry of Unsaturated Hydrocarbons in Titan's Atmosphere

夏威夷大学的Ralf Kaiser、佛罗里达国际大学的Alexander Mebel和韦恩州立大学的Arthur Suits共同支持了一个研究项目，该项目探索低温环境中不饱和碳氢化合物的形成和生长机制。与法国雷恩大学的Ian Sims合作，他们将使用一系列技术，包括电子结构理论、多质量离子成像、交叉光束实验和动力学研究，在将深入了解太阳系外太阳系泰坦、原地球和富含碳氢化合物的行星及其卫星的大气化学的条件下，揭示乙炔自由基反应。多方面的研究目标包括：1)利用无烃交叉分子束机研究单碰撞条件下导致烃类生长的碰撞能量依赖的反应动力学；2)阐明无碰撞条件下烃分子的光解离动力学，鉴定所有产物和分支馏分；3)通过在准直的超冷气体流动中进行反应，揭示乙炔自由基与不饱和烃分子反应的低温动力学；4)利用从头算/统计理论计算来研究广泛的碰撞能量、温度、压力和波长范围内的乙炔自由基反应和光解过程，并在那些观察到非统计效应的系统中，与Joel Bowman(埃默里大学)合作开展更多的动力学研究；以及5)与Yuk Yung(加州理工大学)合作，将这些发现应用到化学反应网络中，对土卫六大气中的碳氢化合物生长进行模拟，并将模型预测与卡西尼-惠更斯卫星前往泰坦的公开数据以及由合作者Alan Tokunaga(夏威夷大学)提供的天文观测数据进行比较。然后，可以对模型进行改进，直到泰坦大气中碳氢分子的预测浓度和观测浓度之间达成一致，并出现基本化学物质的连贯图景。碳氢自由基，如乙炔、C2H，是行星及其卫星(如土卫六)富含碳氢化合物的大气中重要的、高活性的中间体。通过在实验室环境中了解这些自由基的化学动力学和反应，以及通过研究碳氢分子的光化学，将深入了解土卫六(土星的卫星，具有稠密的冷、氮和甲烷大气)上的有机雾层的化学和大气的演变。该项目的其他更广泛的影响包括反应动力学和天体化学方面的跨学科培训、科学讲习班以及对一批不同的初级研究人员的培训。一个公共网站将提供虚拟实验室之旅以及化学反应动力学和天体化学领域的介绍。该项目由化学合作研究(CRC)计划和国际科学与工程办公室资助。

Ralf Kaiser (University of Hawai'i), Alexander Mebel (Florida International University) and Arthur Suits (Wayne State University) are jointly supported for a research project exploring the formation and growth mechanisms of unsaturated hydrocarbons in low temperature environments. In collaboration with Ian Sims, University of Rennes (France) they will use an array of techniques including electronic structure theory, multimass ion imaging, crossed beam experiments, and kinetic studies to unravel ethynyl radical reactions under conditions that will give insight into the atmospheric chemistry on Titan, proto Earth, and hydrocarbon-rich planets and their satellites in the outer Solar System. The multi-faceted research goals include 1) to investigate the collision energy dependent reaction dynamics leading to hydrocarbon growth under single collision conditions employing a hydrocarbon-free crossed molecular beams machine; 2) to elucidate the photodissociation dynamics of hydrocarbon molecules under collision-free conditions, identifying all products and branching fractions; 3) to reveal the low temperature kinetics of ethynyl radical reactions with unsaturated hydrocarbon molecules by carrying out the reactions in a collimated flow of ultra-cold gas; 4) to use ab initio/statistical theory calculations to investigate ethynyl radical reactions and photodissociation processes over a broad range of collision energies, temperatures, pressures, and wavelengths, and in those systems where non-statistical effects are observed, to pursue additional dynamics studies in collaboration with Joel Bowman (Emory University); and 5) to apply these findings to chemical reaction networks in collaboration with Yuk Yung (Caltech), modeling the hydrocarbon growth in the atmosphere of Titan and comparing the model predictions with publicly available data from the Cassini-Huygens mission to Titan and with astronomical observations provided by collaborator Alan Tokunaga (University of Hawai'i). The models can then be refined until an agreement between predicted and observed concentrations of hydrocarbon molecules in Titan's atmosphere is reached and a coherent picture of the underlying chemistry emerges. Hydrocarbon radicals such as ethynyl, C2H, are important, highly reactive intermediates in hydrocarbon-enriched atmospheres of planets and their moons such as Titan. By understanding the chemical dynamics and reactions of these radicals in a laboratory setting, and by investigating the photochemistry of hydrocarbon molecules, insight will be gained into the chemistry of the organic haze layers on Titan (a moon of Saturn with a dense cold, nitrogen and methane-based atmosphere) and the evolution of that atmosphere. Other broader impacts of this project include interdisciplinary training in reaction dynamics and astrochemistry, scientific workshops, and training of a diverse group of junior researchers. A public web site will offer virtual laboratory tours as well as an introduction to the fields of chemical reaction dynamics and astrochemistry. This project is funded by the Collaborative Research in Chemistry (CRC) Program and the Office of International Science and Engineering.