Unidentified interstellar infrared bands: Amorphous hydrogenated carbon a-C:H as a carrier?

A comparison of infrared data on the spectral properties of amorphous hydrogenated carbon (a-C:H) and unidentified infrared (UIR) emission features observed in interstellar spectra shows that the main UIR features can all be explained by assuming that a-C:H particles are their carrier. The frequencies of vibrational a-C:H lines closely match the frequencies of the main unidentified interstellar IR emission bands. The available factual data on the optical properties of a-C:H also allows the observed intensity ratios of the UIR lines to be explained. If this assumption about the UIR carrier is valid, then the estimate of carbon balance in the interstellar medium must be changed. One of the important implications is the inference that a considerable fraction of solid material in the interstellar medium could be produced by the CVD process, which is stimulated by the pumping of energy into a gaseous phase and which differs fundamentally from ordinary condensation.