Infrared spectroscopy is used to study the vibrational frequencies of molecules, such as carbon dioxide CO2 . CO2 is a linear molecule with three atoms and has 4 vibrational modes: two bending modes and two stretching modes. The vibrational frequencies of CO2 are as follows:1. Symmetric stretching mode 1 : This mode occurs at approximately 1330 cm. In this mode, both oxygen atoms move away from or towards the central carbon atom simultaneously, and the net dipole moment of the molecule does not change. Therefore, this mode is not IR active and cannot be observed in the infrared spectrum.2. Bending mode 2 : This mode occurs at approximately 667 cm. In this mode, the oxygen atoms move in a plane perpendicular to the molecular axis, causing a change in the dipole moment. This mode is IR active and can be observed in the infrared spectrum.3. Asymmetric stretching mode 3 : This mode occurs at approximately 2349 cm. In this mode, one oxygen atom moves away from the central carbon atom while the other moves towards it, causing a change in the dipole moment. This mode is IR active and can be observed in the infrared spectrum.4. Another bending mode 4 : This mode is degenerate to the 2 mode and occurs at the same frequency of approximately 667 cm.So, the observed IR active vibrational frequencies of CO2 are approximately 667 cm bending modes and 2349 cm asymmetric stretching mode .