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Paper: Polycyclic Aromatic Hydrocarbons and Infrared Astrophysics: The State of the PAH Model and a Possible Tracer of Nitrogen in Carbon-rich Dust
Volume: 309, Astrophysics of Dust
Page: 665
Authors: Hudgins, D.M.; Allamandola, L.J.
Abstract: Over the past fifteen years, thanks to significant, parallel advancements in observational, experimental, and theoretical techniques, tremendous strides have been made in our understanding of the role aromatic materials play in the interstellar medium (ISM). Twenty years ago, the possible existence of an abundant population of large, carbon-rich molecules in the ISM was unthinkable. Today, the unmistakable midinfrared (mid-IR) spectroscopic signatures of polycyclic aromatic hydrocarbon molecules (PAHs) - shockingly large molecules by the standards of traditional interstellar chemistry - are recognized throughout the Universe. Indeed, it is through these observations and more than a decade of laboratory IR spectroscopic studies that the interstellar PAH model was founded and gained the wide acceptance it enjoys today. Moreover, it is the model's solid foundation in the mid-IR that has driven a wide range of studies into the possible impact of PAHs in the ultraviolet, visible, near-IR, and radio regions of the electromagnetic spectrum as well as their chemical characteristics under interstellar conditions. In this paper, we will examine the current state of the interstellar PAH model as it relates to the ubiquitous interstellar IR emission and its emerging ability to exploit those features as a diagnostic tool to derive insight into the nature of the interstellar PAH population. As an example of this application, we will examine the results of our recent spectroscopic studies of polycyclic aromatic nitrogen heterocycles (PANHs) - PAHs with an atom of nitrogen substituted into the aromatic skeleton - and discuss a possible tracer of such species amongst the interstellar PAH emission bands in the latest observational data.
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