2013/09/30 by Yacine Ali-Haïmoud · 2 citations
Chemistry · Earth and Planetary Sciences · Physics and Astronomy · #Angular momentum #Astrochemistry #Astronomy #Astrophysics #Astrophysics and Star Formation Studies #Atmospheric Ozone and Climate #Corannulene #Emission spectrum #Galaxy #Interstellar medium #Molecular Spectroscopy and Structure #Molecule #Physics #Rotational spectroscopy #Rotational transition #Spectral line #Spectroscopy #astro-ph.GA
paper · pdf · doi:10.1093/mnras/stt2083
published as MNRAS, 437, 2728 (2014) · Version accepted for publication in MNRAS, after minor revisions
arxiv created 2013/10/24 · openalex publication_date 2013/12/03 · arxiv updated 2015/08/21 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/06
Polycyclic aromatic hydrocarbons (PAHs) are believed to be ubiquitous in the interstellar medium. Yet, to date no specific PAH molecule has been identified. In this paper, a new observational avenue is suggested to detect individual PAHs, using their rotational line emission at radio frequencies. Previous PAH searches based on rotational spectroscopy have only targeted the bowl-shaped corannulene molecule, with the underlying assumption that other polar PAHs are triaxial and have a complex and diluted spectrum unusable for identification purposes. In this paper, the rotational spectrum of quasi-symmetric PAHs is computed analytically. It is shown that the asymmetry of planar, nitrogen-substituted symmetric PAHs is small enough that their rotational spectrum, when observed with a resolution of about a MHz, has the appearance of a ‘comb’ of evenly spaced stacks of lines. The simple pattern of these ‘comb’ spectra allows for the use of matched-filtering techniques, which can result in a significantly enhanced signal-to-noise ratio. Detection forecasts are discussed for regions harbouring ‘anomalous microwave emission’, believed to originate from the collective PAH rotational emission. A systematic search for PAH lines in various environments is advocated. If detected, PAH ‘combs’ would lead us to the conclusive and unambiguous identification of specific, free-floating interstellar PAHs.