FIRST INFRARED BAND STRENGTHS FOR AMORPHOUS CO2, AN OVERLOOKED COMPONENT OF INTERSTELLAR ICES

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-CO2 IR band shapes and positions also is investigated, and the three discordant reports of amorphous CO2 spectra 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 CO2 ices, all ices being made near 10 K, are not for amorphous CO2, but rather for crystalline CO2 or crystalline-amorphous mixtures.

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