Representative IR spectrum taken after deposition at 15 K (blue) of the 1:24 ¹³CH₃OH:CO mixture and during the TPD at 100 K (red), showing the main IR features of CO and ¹³CH₃OH. For the methanol CO stretch mode, the ¹³CO and CO peak (cut-off due to its high peak intensity) are visible. Between the two CO peaks an artefact, labelled int., is visible caused by the high intensity of the CO peak.