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E.L.O. Bakes (SETI Institute/NASA ARC), A.G.G.M. Tielens (SRON), C.W. Bauschlicher, D.H. Hudgins, L.J. Allamandola (NASA ARC)
IR emission features at 3.3, 6.2, 7.7, 8.6, 11.2 microns and 12.7 microns are observed in many astronomical sources at various stages of evolution. These mysterious features are generally attributed to polycyclic aromatic hydrocarbon (PAH) molecules, although exact identification of the carriers of these IR features with specific molecules has remained elusive. We have made substantial inroads into clarifying the nature of the carriers of the ``UIR'' emission. The useage of quantum chemistry has taken the prediction of IR emission and the chemical evolution of PAHs to a superior level of theory surpassing former studies. We believe the answer to one of the key questions in astrophysics, ``What is the nature of the carriers of the UIR emission features?'' is within our grasp. In this talk, we will present how we have explained the longstanding problem highlighted by low resolution observational results from ISO as to why the ``UIR'' features show little variation across the face of our own and other galaxies. We will go on to explain why ``UIR'' features observed at high spatial resolutions show substantial localised variations in heavily UV irradiated star forming regions. We will show how we have helped constrain the charge, size, molecular structure, degree of hydrogenation, effects of molecular sidegroups and possible molecular asymmetry of the ``UIR'' carriers. Our work has shown a compelling match to ISO observations of the surface of the Orion PDR and using quantum chemically synthesised IR spectra from C96H24, the largest PAH currently studied, we will demonstrate how PAHs of size greater than 80 carbon atoms are important for explaining the ``UIR'' emission.
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Bulletin of the American Astronomical Society, 34
© 2002. The American Astronomical Soceity.