X-ray photodesorption spectra from mixed ices. Top panels: X-ray photodesorption yields of ¹³CO near the N K edge and of CH₃CN near the O K edge (squares with error bars) from a mixed ¹³CO:CH₃CN ice at 15 K, with dilution ratios of 1:1 (blue) and 7:1 (red). The yields were measured for a fresh ice at 15 K having received a photon fluence < 1 × 10¹⁶ photons cm⁻². The TEYs, measured at higher fluences (5–10 × 10¹⁶ photons cm⁻²), are displayed as dashed lines. Bottom panels: X-ray photodesorption spectra (blue) of the m/z 44 from a ¹³CO:CH₃CN (1:1) ice near the N K edge (left panel) and of the m/z 28 from a H₂O:CH₃CN (1: 1) ice near the O K edge (right panel). In red we also display the TEYs. The photodesorption signals and the TEYs were measured simultaneously at 15 K. The Y-scale of the bottom panels is in arbitrary units.