Speaker
Description
Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous ingredients of the interstellar medium where they contain 15 to 20% of all the carbon and play a crucial role in the ionization balance and gas heating (Tielens et al., 2008). PAHs produce bright emission spectral features called the Aromatic Infrared Bands (AIBs), which are detected in great detail thanks to the exquisite spectral resolution of the James Webb Space Telescope. This new and very informative data calls for a more sophisticated emission model for PAHs that considers important properties such as anharmonicity. ALPAHCAS (Anharmonic Level calculations of PAH Cascade emission and Absorption Spectra), an open-source package which builds upon code developed by Mackie et al. (2018), can calculate detailed absorption and emission spectra of PAHs based on Density Functional Theory (DFT). To assess the quality of our DFT calculations, we performed a benchmark of different model chemistries against the experimental absorption spectrum of the pyrene cation obtained at the HFML-FELIX (Panchagnula et al., 2020). We find that our optimal model chemistry (B3LYP/N07D) shows a very good agreement with the experiment, with an absolute average deviation of 2.6 nm (relative deviation of 0.29%) and a maximum deviation of 9.6 nm (relative deviation of 1.1%). This is then used to compute the emission spectrum, where we can reproduce spectral signatures and their features as seen in JWST observations. In future work, ALPAHCAS will be expanded to include more photophysical processes, and will be used to calculate spectra of larger cationic PAHs to construct a size tracer for relevant astronomical environments. This Project is financially supported by the Dutch Astrochemistry Network of the Dutch Research Council (NWO) under grant no. ASTRO.JWST.001.
| Talk category | NOVA Network 2 |
|---|---|
| Second preference | Plenary |
| PhD relevance | 2nd |
