RAIR difference spectra from a co-deposition of H and ¹⁶O₂ from Cuppen et al. (2010), H₂, CO₂ and ¹⁸O (experiment 1), CO₂ and ¹⁸O (experiment 2). Spectra are baseline corrected and offset for clarity. The spectra corresponding to experiments 1, 2 and 5 are scaled with a factor 3. Note that the multitude of peaks in the right panel for experiments 1 and 2 are due to water vapor in the setup, and the peaks at 3515 and 3564 cm^-1 are also visible in a “pure” CO₂ spectrum.