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

Area of Science:

• Astrochemistry
• Materials Science
• Planetary Science

Background:

• Propionitrile is an astronomical molecule relevant to Titan's atmospheric and surface conditions.
• Understanding its structural properties and thermal expansion is key to modeling icy systems in the outer Solar System.

Purpose of the Study:

• To determine the crystal structure and thermal expansion of propionitrile.
• To provide data crucial for computational modeling of propionitrile-ice systems.
• To aid in the simulation and assignment of infrared spectral peaks for planetary astronomy.

Main Methods:

• Synchrotron powder X-ray diffraction was used to analyze propionitrile.
• Experiments were conducted in the temperature range of 100–150 K.
• Crystallographic data, including unit cell parameters, were collected.

Main Results:

• Propionitrile crystallizes in the Pnma space group.
• Unit cell parameters at 100 K were determined: a = 7.56183(16) Å, b = 6.59134(14) Å, c = 7.23629(14) Å.
• Highly anisotropic thermal expansion was observed, with an eightfold increase along the c-axis compared to the b-axis.

Conclusions:

• The determined structural and thermal expansion data are essential for accurate computational modeling.
• These findings will enhance the interpretation of infrared spectra from outer Solar System bodies.
• The study provides critical insights into the behavior of propionitrile under conditions relevant to Titan.