X-ray photodesorption QMS signals of m/z 27 from pure CH₃CN ice (top part) and of m/z 41 from mixed ¹³CO:CH₃CN (10:1) ice (bottom part), both irradiated at 15 K and at a fixed photon energy for a few tens of seconds. The fixed energies at which the ice is irradiated are indicated in red for each irradiation step. The QMS signals are scaled for more clarity, meaning that the relative intensities between the m/z 27 and 41 signals do not represent the actual ones.