Collection of mid-infrared transmission spectra in the 1600 to 800 cm⁻¹ (6.25 to 12.5 μm) region of binary CH₃OH : X ices (left panel) and ternary H₂O : CH₃OH : X (centre panel) and CO : CH₃OH : X (right panel) ices, where X ∈ {CH₃OD, CH₂DOH, CHD₂OH, CD₃OH, CD₃OD}. Each panel presents spectra acquired at three increasing concentrations of X (9 %, 50 %, and 66 % for binary mixtures; 5 %, 25 %, and 33 % for ternary mixtures). Highlighted spectral regions (A–F) indicate the characteristic double-peak features of CH₂DOH and CHD₂OH in different ice environments, analysed further in Fig. C.2. All spectra were recorded at 10 K and are vertically offset for clarity. Additional experimental details are provided in Appendix C.