Integrated areas of the doublets marked in regions A–F of Fig. C.1. Panels A–F correspond to the same spectra shown in Fig. C.1. For each spectral window, the two peak components were integrated separately as a function of increasing deuterated methanol concentration, and the resulting band areas were plotted against the total fraction of CH₂DOH and CHD₂OH in the ice, showing an approximately linear dependence across all mixture types.