Spectra of two H₂O:NH₃:H₂S mixtures at 15 and 135 K. The plot insets zoom in on two features of interest in this work, the SH⁻ stretching mode and the NH₄⁺ asymmetric bending (ν₄) mode. The dashed vertical lines within the right inset indicate the peak positions of the NH₄⁺ ν₄ mode at the two plotted temperatures, showing how the feature redshifts as the ice is heated. Vibrational mode assignments are provided for the H₂O:NH₃:H₂S mixture at 135 K.