infrared spectra in the range of 1550–1390 cm⁻¹ (6.45–7.19 μm) showing the CH₃ asymmetric deformation 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. Since the FWHM of the CH₃ asymmetric deformation band was not measured in the methanol-containing mixtures (due to the overlap with the methanol CH₃ bending mode), the peak position vs. FWHM plot for this acetone feature in CO matrix is displayed with the data in Fig. A.9.