The structure of solid phosphorus pentabromide

The Raman frequencies of solid phosphorus pentabromide, excited by the green and yellow mercury lines, are: 72(6), 140(14), 189(0+), 227(26), 367(2−) and 474(9). 72(v2.3), 140(v4,5,6), 227(v1) and 474(v7,8,9) are the fundamental vibrations of the nearly regular tetrahedron ‐formed by the group PBr4+, which together with Br− build up the lattice of solid PBr5. The force constants according to the Urey‐Bradley field are: K1 = 2.19, K2 = 0.18 and γ3 = 0.028 all in 105 dynes/cm. The corresponding values for SiBr4, isoelectronic with PBr4+, are 1.99, 0.12 and 0.11 × 105 dynes/cm.