Upper panel: infrared spectra in the range of 520–580 cm⁻¹ (19.2–17.2 μm) showing the CO in-plane deformation band of acetone in different ice mixtures, from left to right: pure CH₃COCH₃,CH₃COCH₃:CH₃OH(1:5), CH₃COCH₃:CO(1:5), and CH₃COCH₃:CH₃OH:CO(1:2.5:2.5). The spectra at different temperatures are offset for improved visualization. Bottom left: peak position vs. FWHM plot for the CO in-plane deformation 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 CO in-plane deformation band at 15 K in the various matrices with respect to the band strength for pure acetone from Hudson et al. (2018).