Raman Scattering as the Key Link Between Unidentified Infrared Bands, Diffuse Interstellar Bands, and Extended Red Emission

Understand

This paper calls attention to the relevance of Raman scattering by atomic hydrogen to three optical and near/mid-infrared spectral features of HI clouds: extended red emission (ERE), diffuse interstellar bands (DIBs), and the unidentified infrared bands (UIBs).

• DIBs, ERE, and UIBs are observed predominantly at the edge of HI clouds, are manifestly related, and remain poorly understood.
• Their salient properties correspond to two major characteristics of HI Raman scattering: unusual line broadenings and a concentration of the Raman scattered ultraviolet continuum in the vicinity of hydrogen's optical and infrared transitions.
• Raman scattering by atomic hydrogen has now been detected in several object classes where the spectral features are observed, and I argue that it can account for all three features.