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Anisotropic thermal expansion of the acetylene–ammonia co‐crystal under Titan's conditions
Author(s) -
Vu Tuan H.,
Maynard-Casely Helen E.,
Cable Morgan L.,
Hodyss Robert,
Choukroun Mathieu,
Malaska Michael J.
Publication year - 2020
Publication title -
journal of applied crystallography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.429
H-Index - 162
ISSN - 1600-5767
DOI - 10.1107/s1600576720014028
Subject(s) - titan (rocket family) , thermal expansion , orthorhombic crystal system , anisotropy , ammonia , negative thermal expansion , crystal structure , chemistry , crystallography , acetylene , atmospheric temperature range , materials science , thermodynamics , astrobiology , organic chemistry , physics , optics , composite material
Acetylene and ammonia are known to form a stable orthorhombic co‐crystal under the surface conditions of Saturn's moon Titan (1.5 bar = 150 kPa, 94 K). Such a material represents a potential new class of organic minerals that could play an important role in Titan's geology. In this work, the thermal expansion of this co‐crystalline system has been derived from in situ powder X‐ray diffraction data obtained between 85 and 120 K. The results indicate significant anisotropy, with the majority of the expansion occurring along the c axis (∼2% over the temperature range of interest). Rietveld refinements reveal little change to the structure compared with that previously reported by Boese, Bläser & Jansen [ J. Am. Chem. Soc. (2009), 131 , 2104–2106]. The expansion is consistent with the alignment of C—H…N interactions along the chains in the a and b axes, and weak intermolecular bonding in the structural layers along the c axis.