Upper panel: infrared spectra in the range of 1760–1630 cm⁻¹ (5.68–6.13 μm) showing the C=O stretch band of acetone embedded in different ice mixtures, from left to right: pure CH₃COCH₃, CH₃COCH₃:CH₃OH(1:20), CH₃COCH₃:CO(1:20), and CH₃COCH₃:CH₃OH:CO(1:10:10). The spectra at different temperatures are offset for improved visualization. Bottom left: peak position vs. FWHM plot for the C=O stretch band in different ice matrices, represented by the different colors, and for different temperatures, indicated by the numbers in the graph. Bottom right: apparent band strength for the acetone C=O stretch band at 15 K in the various matrices with respect to the band strength for pure acetone from Hudson et al. (2018).