Polycyclic Aromatic Hydrocarbons (PAHs) are ubiquitous in space and most astronomical spectra are dominated by their ubiquitous infrared emission features (UIBs or "PAH bands" as they are now commonly dubbed). Whether the PAH bands are intimately associated with the object, or foreground/background confounding features, they will have to be understood, separated from other features in the spectra, and analyzed for the information they contain on the physical and chemical properties of their surrounding environments. High-resolution laboratory spectra of PAHs and PAH related species measured in astrophysically-relevant environment are critical to answer these questions. The most challenging task is to reproduce the physical and chemical conditions that are present in space (i.e., cold gas phase molecules and ions, isolated in a collision-free environment). Comparable conditions can be achieved using the cosmic simulation chamber (COSmIC) developed at NASA Ames. COSmIC allows to measure gas phase spectra of neutral and ionized interstellar PAH analogs by associating a molecular beam with a soft ionizing discharge that generates a cold plasma expansion (≈100 K). Using the highly sensitive Cavity Ring Down Spectroscopy (CRDS) technique, absorption spectra of PAHs and PAH derivatives seeded in Ar supersonic expansion are measured in the NUV-Vis-NIR region [Salama, F., Galazutdinov, G. A., Krelowski, J., Biennier, L., Beletski, Y. and Song, I.-O. (2011), The Astrophys. J. 728, 154]. The resulting spectra provide a critical tool to identify and characterize specific molecules or ions in astrophysical environments. We intend to expand the capabilities of our current CRDS system to the NIR and MIR up to 3.5 µm in order to provide accurate high-resolution laboratory spectra that will help validate the extensive NASA Ames’ PAH database (PAHdb) and will greatly benefit the interpretation of future JWST NIRSpec observational data. We also intend to implement two highly sensitive optical diagnostics, Laser Induced Fluorescence (LIF) and Laser Induced Incandescence (LII) in COSmIC in order to investigate the emission spectral signatures of cosmic molecules and grain analogs. The emission database of PAHs, PAH derivatives, PAH-clusters, and nanoparticles in the UV-NIR region is highly needed to assess the hypothesis of PAHs and PAH-related species as carriers of the blue luminescence, the extended red emission, and cometary emission.

High-resolution supersonic jet spectroscopy of interstellar PAHs and PAH-related analogs:  Astronomical applications

256th National Meeting (2018)

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