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.
The goal of our NSF-CRC project has been to understand the underlying mechanisms on the synthesis of complex, hydrogen-deficient hydrocarbons on the molecular level in low temperature environments, and to apply these findings to better comprehend the chemical processes leading to the organic, hydrocarbon-based haze layers in the atmosphere of Saturn’s moon Titan. To achieve these goals, we developed a tightly integrated collaborative network by combining fundamental studies in experimental physical chemistry exploiting the power of single collision conditions with electronic structure theory and chemical modeling of Titan’s atmosphere. Our project has been extremely productive not only scientifically, but also from the standpoints of human resource development and educational outreach. We revealed the underlying reaction mechanisms, dynamics, and kinetics of several key reaction classes forming complex (≥ C4) molecules relevant to the chemical processing of Titan’s organic aerosol layers: polyynes, (polycyclic) aromatic hydrocarbons (PAHs), resonantly stabilized free radicals (RSFRs), cyanopolyynes, and nitrogen-bearing (polycyclic) aromatic hydrocarbons (N-PAHs) thus effectively coupling Titan’s hydrocarbon and nitrogen chemistry. We further trained 22 scientists (12 undergraduate students,9 graduate students, and 12 postdoctoral fellows, of which 6 belong to underrepresented groups) in the fields of chemical dynamics, chemical kinetics, theoretical chemistry, and planetary chemistry. Our co-mentoring, collaborative training, and (international) mobility of the network researchers resulted in 63 visits to laboratories, workshops, and conferences. We feel that these data demonstrate our sincere efforts to contribute significantly to the training and education of scientists capable of assuming leading roles in US science in the future. To disseminate the results to the community, the PI and CoIs have been organizing annual, three-day long interdisciplinary workshops on ‘Titan’s Chemistry – Observations, Experiments, Computations, and Modeling’ held across the US and in Europe in Honolulu (2007), Miami (2008), San Juan (2009), Abbaye de St Jacut de la Mer (France) (2010), and Kauai (2011) with typically 50 to 60 participants per workshop. These meetings brought together experimental and theoretical chemists with planetary scientists, astronomers and modelers. Note that the third Titan workshop (2009) led to a special issue of JPCA featuring a collection of contributions arising from the workshop; the fourth workshop was organized primarily by the Rennes team following the Faraday Discussion 147 ‘Chemistry of the Planets’ chaired by IRS. This enabled us to attract a particularly wide range of participants to the NSF workshop. All Titan meetings were immensely successful at bridging the disciplinary boundaries that separate these communities, with the result that a higher level of science was achieved across all of these fields. Research results from our network were also disseminated to teachers, high schools, and to the public. For example, PI presented lectures in Astrochemistry and Astrobiology (2007-) at teacher workshops at the University of Hawaii. At these occasions, lab tours were also conducted so that the instructors could ‘see’ how modern research in chemistry and astrobiology is being conducted. This in turn enables educators to incorporate research into school and college teaching. Further, our paper by X. Gu et al. on the possible formation of building blocks of the organic aerosol layers on Titan entitled Chemical dynamics of triacetylene formation and application to Titan's atmosphere published in The Proceedings of the National Academy of Sciences U.S.A. [106, 16078-16083 (2009)] generated substantial public interest. It was featured, for instance by Chemistry World (RSC, UK), CEN (ACS) as well as national and international newspapers. AGS presented lectures on "Chemistry in Space" to elementary schools (Ann Arbor Open School), to amateur astronomy groups (University Lowbrow Astronomers) and to an adult education class (Chelsea Adult Learners).
