Raman Scattering by Atomic Hydrogen in Photodissociation Regions: An Alternative to the Polycyclic Aromatic Hydrocarbons Hypothesis

Abstract Photodissociation regions (PDRs) illuminated by high temperature ( T > 10 4 K) radiation fields display characteristic optical to midinfrared spectral features: emission bands that cluster around the blue limits of hydrogen series, an extended red (ERE) in vicinity H α , and a continuum infrared part spectrum only. The footprint ERE its intensity at maximum unequivocally designate Raman scattering photons near Ly β as responsible for feature, thus suggesting PDR spectra be considered spectra. This finding challenges currently accepted hypothesis yet-to-be-identified complex carbonaceous molecules, such polycyclic aromatic hydrocarbons, are source PDRs’ unidentified bands. It has, therefore, significant implications field astrochemistry.