Publication
- Names
-
- Reggie L. Hudson
- Title
- Preparation, identification, and low-temperature infrared spectra of two elusive crystalline nitrile ices
- Abstract
- Infrared (IR) spectra of the alkyl nitrile ices CH$_3$CN and CH$_3$CH$_2$CN are relevant to the study of the low- temperature chemistry of objects within and beyond the Solar System, but the thermodynamically favored low-temperature crystalline phases of these compounds have not been presented and identified in the planetary-sciences literature. Moreover, there is a large variation in the published IR spectra of these two icy solids, including spectra that are used for the analyses of spacecraft data from the Voyager and Cassini missions. Here the IR spectra of the low-temperature crystalline forms of CH$_3$CN and CH$_3$CH$_2$CN, which are the thermodynamically stable phases at Titan temperatures, are presented for the first time with all samples being made by vapor-phase deposition. Conditions are described for producing these ice phases for both compounds, and new measurements are reported of ice density and refractive index, quantities needed to compute IR absorption coefficients, band strengths, optical constants, and, ultimately, nitrile abundances in extraterrestrial environments. Comparisons are drawn between CH$_3$CN and CH$_3$CH$_2$CN, an earlier prediction on their similar crystallization behaviors is verified, and previous work is examined in light of these new results, including a counter-intuitive observation in which the low- temperature phase of an ice is made by heating a high- temperature phase. Applications and extensions are described.
- Keywords
- spectroscopy, absorbance spectra, data analysis, band position, band vibration mode, mid-IR, amorphous, crystalline, phase transition, molecular solid, nitrile, CH3CN, CH3CH2CN, acetonitrile, propionitrile, Titan
- Content
- spectral data, band list data, phase
- Document type
- article
- Publication state
- published
- Doi
- 10.1016/j.icarus.2019.113548
- Identifiers
-
- bibcode: 2020Icar..33813548H