CRC: Chemistry of Unsaturated Hydrocarbons in Titan's Atmosphere

University Of Hawaii, Honolulu

Investigators

Abstract

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.