Raman and infrared spectra of solid tin tetrabromide

Abstract

Raman and infrared spectra of crystalline tin tetrabromide at temperatures between 20 K and the melting point, 304 K, are reported. No evidence of any solid-state phase transition was found. Splittings of the four molecular modes are discussed in terms of crystal field effects and isotopic species. All twelve Raman and five of the nine infrared-active lattice modes, predicted on the basis of a group theoretical analysis, have been observed. Since these peaks lie within a relatively narrow frequency range, and since the molecules are located on general sites in the unit cell, mixing between modes is likely to be considerable.

Lattice Dynamics of Tin Tetrabromide

“…For the symmetric stretch, vl, the tin atom is stationary. Splittings from the bromine isotopes are between 0.6 and 0.7 cm-l and these have been observed in a recent study [7], together with additional crystal field effects to be discussed later. For the degenerate stretch, v3, the separation between the two extreme peaks resulting from different bromine isotopes (SnBr:' and SnBrlg) is only 0.9 em-1, while the additional splittings resulting from loss of degeneracy cover a range of up to 1.8 cm-l. For the principal tin isotopes, separations of up to 1.2 em-1 are found.…”

“…There have been several spectroscopic studies of solid SnBr,, details of which have been given in a recent paper [7], which also presented Ranian and far infrared data on samples a t temperatures between 20 K and the melting point, 320 K. This investigation established that there is no solid state phase transition over this temperature range. Of the 36 internal mode components, a total of 32 (16 each in Raman and infrared spectra), not including additional isotopic peaks, were observed.…”

“…The form of these modes has been illustrated by Herzberg [$I. Their frequencies are well established from Raman and infrared spectra of solutions, as discussed in an earlier paper [ 7 ] . For comparison with the calculations to be presented here, we will use those selected by Shimanouchi [9].…”

“…We have chosen to tackle this problem rather than simpler extensions of the model to, for example, other diatomics and triatomics, because recent spectroscopic studies of tetrahalide crystals [4 to 61 have shown that assignment of the observed lattice modes is extremely difficult in the absence of a lattice dynaniical representation. I n particular, a detailed Raman and far infrared investigation of solid SnBr, [ 7 ] determined most of the lattice frequencies as well as multiple peaks for the intramolecular modes, caused by isotopic species, distortions of the molecules, and crystal field effects. It is hoped that the present calculations will allow a detailed assignment of these spectra and, by extension, provide a more complete understanding of the vibrations of other tetrahalide crystals with similar structures.…”