2015ApJ...808L..40G

Solid carbon dioxide (CO₂) has long been recognized as a component of both interstellar and solar system ices, but a recent literature search has revealed significant qualitative and quantitative discrepancies in the laboratory spectra on which the abundances of extraterrestrial CO₂ are based. Here we report new infrared (IR) spectra of amorphous CO₂-ice along with band intensities (band strengths) of four mid-IR absorptions, the first such results in the literature. A possible thickness dependence for amorphous-CO₂IR band shapes and positions also is investigated, and the three discordant reports of amorphous CO₂spectra in the literature are addressed. Applications of our results are discussed with an emphasis on laboratory investigations and results from astronomical observations. A careful comparison with earlier work shows that the IR spectra calculated from several databases for CO₂ices, all ices being made near 10 K, are not for amorphous CO₂, but rather for crystalline CO₂or crystalline-amorphous mixtures.