Crystal structure of propionitrile (CH3CH2CN) determined using synchrotron powder X‐ray diffraction

The structure and thermal expansion of the astronomical molecule propio­nitrile have been determined from 100 to 150 K using synchrotron powder X-ray diffraction. This temperature range correlates with the conditions of Titan's lower stratosphere, and near surface, where propio­nitrile is thought to accumulate and condense into pure and mixed-nitrile phases. Propio­nitrile was determined to crystallize in space group, Pnma (No. 62), with unit cell a = 7.56183 (16) A, b = 6.59134 (14) A, c = 7.23629 (14), volume = 360.675 (13) A3 at 100 K. The thermal expansion was found to be highly anisotropic with an eightfold increase in expansion between the c and b axes. These data will prove crucial in the computational modelling of propio­nitrile–ice systems in outer Solar System environments, allowing us to simulate and assign vibrational peaks in the infrared spectra for future use in planetary astronomy.