Far-Infrared and Raman Spectra of Phosphonium Bromide and Phosphonium Bromide-d4

The infrared spectra of thin films of PH₄Br and PD₄Br have been recorded from 33 to 4000 cm⁻¹ at − 170°C. Raman spectra of polycrystalline samples were also recorded at − 170°C. Three librations and two translations have been assigned for both compounds, and eight internal fundamentals were observed. Other bands found in the infrared and Raman spectra were attributed to overtones and combinations involving external and internal fundamentals. Static field and correlation field splittings of 25 and 11 cm⁻¹, respectively, were observed for PH₄Br. The barriers restricting phosphonium ion rotation in the respective lattices were calculated from the observed librational frequencies and the barrier height for the PH₄ ion is 7.8 kcal/mole $\text{(ν\hspace{0.17em}=\hspace{0.17em}354}{\mathrm{cm}}^{\text{−1}})$ and for the PD₄ ion is 7.9 kcal/mole $\text{(ν\hspace{0.17em}=\hspace{0.17em}254}{\mathrm{cm}}^{\text{−1}})$ .