Abstract
The two phonon Raman spectrum of KBr is calculated. The calculation is based on the shell model and assumes a nonlinear coupling between the shell and the core of the negative ions. It is found that the results are considerably improved by using a breathing shell model rather that a rigid shell model. The theory then contains three parameters which may be chosen to give a reasonable description of the experimental results. An investigation of the importance of inter-ionic nonlinearities suggests that they are far less important for describing Raman scattering than are the intra-ionic terms.