In the Fig. , we can see the main peak at 668.5 cm -1 . Thanks to the discussion by , we can link this peak to the C-S stretching mode. In the Figure we can also see the shoulder at 630.8 cm -1 , related to the COO-wagging. In the following Fig. , we consider the fit of the second most relevant peak, that at 894 cm -1 (see Fig. ). For the Figures and, we considered two frequency ranges fitted independently from each other (see discussion in Appendix). Now, let us investigate the frequency range between them.