Propane and propane–water interactions: a study at cryogenic temperatures

Abstract

The phase transition of solid propane and a propane–water mixture under ultrahigh vacuum has been investigated using reflection absorption infrared spectroscopy (RAIRS) and temperature-programmed desorption mass spectrometry (TPD-MS). Here, the investigation is divided into two sections: the phase transition of pure propane and the interaction of propane with water. RAIR spectra of pure propane reveal an unknown crystalline phase at 50 K (phase I), which gradually converts to a known crystalline phase (phase II) at higher temperature. This conversion is associated with certain kinetics. Co-deposition of water and propane restricts the amorphous to crystalline phase transition, while sequential deposition (H₂O@C₃H₈; propane over predeposited water) does not hinder it. For an alternative sequential deposition (C₃H₈@H₂O; water over predeposited propane), the phase transition is hindered due to diffusional mixing within the given experimental time, which is attributed to the reason behind the restricted phase transition.