2001ApJ...558L.129G

We report laboratory emission spectra of hydrogenated amorphous carbon (HAC) in the wavelength range 19 µm<λ<120 µm (525-83 cm^–1) at temperatures between 300°C and 500°C. These spectra show emission features at 21, 27, and ~33 µm (475, 370, and 303 cm^–1) that can be identified with similar bands in the far-infrared spectra of extreme carbon stars, proto-planetary nebulae, and planetary nebulae. It is suggested that HAC is present in these objects but that the chemical composition of this material depends on the evolutionary state. We also detect a number of broad features at wavelengths longer than 40 µm, attributable to chemical groups in HAC. A strong feature is observed at ~60 µm (165 cm^–1) in laboratory spectra and may be present in spectra of the carbon-rich planetary nebula CPD -56°8032. We briefly discuss the nature of the chemical groups responsible for the appearance of these features.