The crystal structure, thermal expansion and far-IR spectrum of propanal (CH3CH2CHO) determined using powder X-ray diffraction, neutron scattering, periodic DFT and synchrotron techniques

Helen E Maynard-Casely; Nikita S Yevstigneyev; Samuel G Duyker; Courtney Ennis

doi:10.1039/d1cp04477j

The crystal structure, thermal expansion and far-IR spectrum of propanal (CH₃CH₂CHO) determined using powder X-ray diffraction, neutron scattering, periodic DFT and synchrotron techniques

Phys Chem Chem Phys. 2021 Dec 22;24(1):122-128. doi: 10.1039/d1cp04477j.

Authors

Helen E Maynard-Casely¹, Nikita S Yevstigneyev², Samuel G Duyker³, Courtney Ennis²

Affiliations

¹ Australian Nuclear Science and Technology Organisation, Locked Bag 2001, Kirrawee DC, NSW, 2232, Australia. helen.maynard-casely@ansto.gov.au.
² Department of Chemistry, University of Otago, Dunedin, 9054, New Zealand.
³ Sydney Analytical, Core Research Facilities, The University of Sydney, Sydney NSW, 2006, Australia.

PMID: 34897323
DOI: 10.1039/d1cp04477j

Abstract

The crystal structure of propanal has been determined using powder X-ray diffraction (PXRD), where this common laboratory aldehyde is measured to crystallise in spacegroup P21/a, Z = 4 with a unit cell a = 8.9833(6) Å, b = 4.2237(2) Å, c = 9.4733(6) Å and β = 97.508(6)°, resulting in a volume of 356.37(4) Å³ at 100 K and atmospheric pressure. The thermal expansion observed from 100 K until the sample melted (∼164 K) was found to be anisotropic. An additional neutron diffraction study was carried out, reaching a temperature of 3 K and found no further phase transformations from the determined structure at lower temperatures. The investigated temperature regime correlates to astronomical surfaces, including outer Solar System bodies and interstellar dust mantles, where propanal is thought to be generated by energetic processing of composite molecular ices. Results from the structure determination were applied to model propanal ice using periodic density functional theory for the calculation of intermolecular frequencies, where the simulated far-infrared spectrum of solid propanal can now be used for future molecular astronomy.