(a) 2750–3000 cm⁻¹ region with spectra of different ices, from left to right: pure CH₃NH₂, CH₃NH₂:H₂O (1:20), CH₃NH₂:CH₄ (1:20), and CH₃NH₂:NH₃ (1:20). The CH₃ symmetric stretch mode of CH₃NH₂ (around 2792 cm⁻¹) lays in the rightmost region in all the panels. (b) Left panel: peak position vs. FWHM for the CH₃ symmetric stretch band in pure and CH₃NH₂:NH₃ (1:10) ices. Right panel: relative band strength of the CH₃ rock vibrational mode in different ice mixtures at 15 K. c same as b for the CH₃ antisymmetric stretch band (around 2881 cm⁻¹) in the ice mixtures displayed in a.