As shown, the peak at around 1.8 THz is predicted for both forms with comparable intensities, hence the decision to normalise the experimental spectra relative to that feature in Figure . The three circled areas correspond to the differences identified between the experimental spectra: (i) the feature at 1.53THz is predicted only for form II, which explains why the peak is more pronounced in the spectra of the form II samples; (ii) the merging of the peaks just below 2.0