Change in the Stable Crystal Phase of Tetra‑<i>n</i>‑butylammonium Bromide (TBAB) Hydrates Enclosing Xenon

This article reports the inversion of the stable phase of tetra-<i>n</i>-butyl ammonium bromide (TBAB) hydrates in the xenon (Xe)–TBAB–water system. In the TBAB solution (mass fraction of TBAB in the water solution, <i>w</i> = 0.40) under atmospheric pressure, the TBAB–water system preferentially forms the TBAB·26H₂O hydrate. Through in situ Raman spectral analysis, the stable crystal phase of the TBAB hydrate enclosing Xe changed from TBAB·26H₂O to TBAB·38H₂O during temperature ramping from 283.6 to 287.4 K at 0.3 MPa. No lattice vibration shift was observed for the TBAB·26H₂O hydrate enclosing Xe, whereas the lattice vibration of the TBAB·38H₂O hydrate enclosing Xe shifted to a lower wavenumber. When conducting temperature ramping in a pressure vessel, it was observed that phase transformation of the TBAB hydrates enclosing Xe occurred at a pressure and temperature higher than 0.2 MPa and 287 K, respectively