Infrared Spectral Intensities of Amine Ices, Precursors to Amino Acids

Here, we address the paucity of infrared (IR) spectral data needed to quantify low-temperature experiments with amine ices, such as the formation of amino acids, by reporting new IR results on solid phases of methylamine (CH₃NH₂) and ethylamine (CH₃CH₂NH₂), precursors to glycine and alanine, respectively. Mid-IR band strengths and absorption coefficients for CH₃NH₂ and CH₃CH₂NH₂, in both amorphous and crystalline forms, are presented, along with measurements of a density and refractive index (670 nm) for each. For these same compounds, we also have calculated IR optical constants, and they are being made available in electronic form. Some applications of our new results are described along with proposals for future investigations. Suggestions are made related to the methods employed in such work, and particularly to the application of Beer's Law to the IR study of compounds of astrobiological interest. Comments are also included on the methods used, and the results presented in a recently published work on amino-acid IR intensities.