The considered peak is carbondioxide from air.

Hi Saif,Thomas is correct: MIL-101 has been invented at the Lavoisier Institute (of the UVSQ, in Versailles), and is able to retain four hundred times its volume of carbon dioxide at room temperature. Moreover, 2360 cm-1 is close to the antisymmetric streching mode of CO2. Cheers.

Hi Saif, the most appropriate answer is Thoma's answer. This peak is assigned to CO2.

Best regards

Thomas is correct. Those bands are so-called R-branch/PO-branch of gaseous carbon dioxide molecules caused by the vibration-Rotation of the molecular motion, rather than pure vibration of the molecule. This form of spectrum is unique in a gaseous sample. I suspect that you obtained the shown spectra at a resolution of 4 or 2 cm-1. However, if you obtain the same spectrum with much higher resolution, say 0.2 or 0.1 cm-1, only the bands around 2360 cm-1 will show extremely sharp bands closely packed. This is the proof that those bands around 2360 cm-1 are from the carbon dioxide gas in the instrument rather than in your sample. This is caused because you did not purge the instrument with nitrogen gas, or use the air dried by a special drier that also takes out carbon dioxide gas from the dried air, or the balance of the degree of purge of the spectrometer is unbalanced when you took the reference spectrum and sample spectrum. By ratioing those two spectra to obtain the transmission spectra shown, the carbon dioxide peak will show up. Do you have an air drier attached to the FTIR spectrometer? If so, obtain the reference spectrum by measuring the time. Close the spectrometer rid and measure exactly 15 min, then start scanning the instrument. After you placed the sample in the spectrometer, again close the rid and measure exactly 15 min, and then start scanning exactly the same number of scans as the reference spectrum. Ratio those two spectra and you will obtain a spectrum with almost no bands (only a weak trace remain) around 2360 cm-1.