Colloquium by Jan Cami, Western University, Canada
The Universe is rich in carbonaceous compounds (molecules and dust grains) that appear in a bewildering variety of sizes, structures, shapes and chemical compositions. Fullerenes, a class of large carbonaceous cage molecules, are a fairly recent addition to the molecular inventory. The best-known member of the family is C60 ("buckyballs"). First detected in 2010 with Spitzer in the otherwise inconspicuous planetary nebula Tc 1, fullerenes have since been discovered in a variety of objects -- from evolved stars to the diffuse ISM, reflection nebulae, young stellar objects, and even meteorites. Fundamental questions remain about how these large, stable molecules form, whether they exist in the gas or solid phase, and what physical processes drive their excitation and IR emission.
In this colloquium, I will discuss what we have learned from detailed and spatially resolved spectroscopic observations of Tc 1 with JWST/MIRI and VLT/MUSE and what they may reveal about fullerene formation itself. The spectra are remarkably rich, and show the clear signatures of neutral C60 and C70 in addition to several weaker features. The fullerenes are clearly in the gas phase, with signatures of 13C isotopic substitution. The fullerenes reside in the H II region -- where it was thought they would not survive but should photo-fragment. Electron attachment -- favoured by the high electron density and C60's strong electron affinity -- allows the molecules to survive; photodetachment then excites them, driving IR emission through a pathway not previously considered. The spectra also show unusual dust features that may be related to the formation of fullerenes. Finally, I will discuss the broader implications for large molecules -- including PAHs—in space.
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Host: Daniel Wolf Savin