Lowering the symmetry group of carbon tetrachloride by high pressure

Abstract

Using the pressure‐induced polarized Raman spectra of carbon tetrachloride up to 22 GPa, a significant anomalous polarization (the depolarization ratio >0.75) was observed. We analyzed it by evaluating the antisymmetric anisotropy distribution of modes in Td and explored the corresponded molecular structure having been translated from Td into a lower symmetry. The P21/c and Pa3 structures of carbon tetrachloride were optimized as a function of pressure to further confirm that the molecules deviated from regular tetrahedra. The C2v and D2 were analyzed to be candidates of the lower symmetry based on group and Landau theory.

Carbon tetrachloride under extreme conditions

“…These changes were observed previously and assigned to the phase III→VI transition. 8 7-14 GPa, no further phase transition was observed, 8,9 which agrees with our data.…”

“…Between 1 GPa and 4.35 GPa, a phase transition appears which would likely be a transition from phase III to phase IV. 8,9 From 4.35 GPa to 7.64 GPa, evidence of another phase transition (which we ascribe to IV→V) manifests (particularly when examining the XRD pattern lines above 14 • ) which complements our Raman data. No significant changes (beyond the compression of unit cell parameters and thus shifting of the XRD lines toward higher angle) appear until 14.4 GPa where new peaks emerge near 5 • , 12.5 • , and 15.5 • which suggests a phase transition somewhere around 14 GPa.…”

“…Due to the complexities associated with rapidly sealing and pressurizing a high vapor pressure liquid that rapidly evaporates, we loaded our sample at 1.3 GPa, which implies that it commenced in Phase III. 10 The ν 2,s (E) vibration 8 near 220 cm −1 (i.e., C-Cl symmetric stretching mode) at ambient pressure has split as expected 8,9 at high pressure. The ν 4,s (F 2 ) vibration (i.e., C-Cl asymmetric bending mode) near 325 cm −1 appears at high pressure except at a higher wavenumber value as do the ν 1,s (A 1 ) modes near 460 cm −1 (i.e., C-Cl symmetric stretching mode) and the ν 1 (Fermi resonance doublet) 9 suggesting that our sample comprised solely CCl 4 .…”

“…9 Between 0.4 and 0.7 GPa the material exists as Phase II which is in the C2/c monoclinic symmetry. 8 Above this pressure, the materials transform into Phase III, which is also monoclinic, P2 1 /c, and Z = 4 symmetry. 8,11 Between 3 and 7 GPa (or above 2.3 GPa 10 ), the compound adopts cubic symmetry (Phase IV) 8 and above 7 GPa, a new phase has been reported 9, 10 that exists at least up to 13 GPa.…”

“…No other phase transitions beyond this were reported up to 22 GPa. 8 As there appears to be some controversy pertaining to the exact number of phase transitions that occur up to 22 GPa, we undertook separate Raman spectroscopic and x-ray diffraction (XRD) a) Author to whom correspondence should be addressed. Electronic mail: pravica@physics.unlv.edu studies with the aim of better-determining the phase/pressure behavior of this important compound with pressure coupled with our infrared study to garner further information on the post reaction products of irradiated CCl 4 .…”