The experimental errors are reported in Figure and Figure upon CO and CO2 adsorption, respectively. Data were collected up to 427 cm -1 . The measurements below 100 cm -1 are not optimized at IN1 and no clear peaks are observed in this region. We note that at low energy the assignation of the vibrational modes from the calculations is more challenging compared to higher energy (see for example the intense peak at 100 cm -1 as compared to that at 400 cm -1 ). While at around 400 cm -1 a good agreement between experiment and DFT is found, low energy modes present larger relative errors possibly due to the underlying approximations (basis set and functional choice may affect this part of the spectra).