(a) Infrared profile of the CH₃ rock vibrational mode of CH₃NH₂, around 1159 cm⁻¹, in different ices, from left to right: pure CH₃NH₂, CH₃NH₂: H₂O(1:5), CH₃NH₂:CH₄(1:5), and CH₃NH₂:NH₃(1:5). The first and the last panels are displayed at a different Y-scale. In the last panel the CH₃NH₂ feature (whose position is indicated by the dashed line) appears as a shoulder in the ammonia ν₂ band (umbrella mode). (b) Left panel: peak position vs. FWHM for the CH₃ rock band in the ice mixtures displayed ina. Different mixtures are indicated by different colors, and the ice temperatures are marked in the graph. Right panel: relative band strength of the CH₃ rock vibrational mode in different ice mixtures at 15 K.