Raman and IR spectra of crystalline phosphine in the γ phase

The γ phase of crystalline phosphine has been studied using IR and Raman spectroscopy. The observations include both pure phases, PH₃ and PD₃, and many of the modes of PH₃, PH₂D and PHD₂ dilute in PD₃ as well as of PD₃, PD₂H and PDH₃ dilute in PH₃. The phase transition β → γ is very slow for PH₃, but much more rapid for PD₃.Evidence is adduced pointing to the existence of inequivalent sites in this crystal, but none of a number of suggested models for the unit cell is entirely consistent with the numbers of multiplet components of the internal modes, nor with the numbers of external (lattice) modes observed in the IR and Raman.