This splitting of modes in the disordered case might also explain the experimental peak at 81 cm -1 in the 83 K experimental spectra that was not well reproduced by the dynamic calculation at 88 K that did not include disorder. Both dynamic calculations predict a similar feature below 80 cm -1 although the relative intensities of the individual peaks varies between the calculations, both calculations over predict the frequency of these modes compared to experiment by 20 cm -1 . The results of Korter et al. do not shed any more light on the lowest frequency peak as the signal at this very low frequency is quite noisy.