CO2Vibrations and IR Spectrum

Energy can be stored in molecules as translational, rotational and vibrational energy. Translation can occur in the x, y or z direction. Rotation can occur around the x, y or z axis, except for linear molecules which only have two axes or rotation. Vibrations involve movements of the atoms of a molecule which produce no net translation or rotation. These various movements are a result of the combination of the normal modes of vibration. For a triatomic molecule these normal modes are symmetric, asymmetric and bending vibrations. In symmetric vibration, the two bonds shorten and lengthen together. In asymmetric vibration, one bond shortens while the other lengthens. In bending vibration, it is the bond angle that oscillates.
This is an IR spectrum of CO2 corresponding to the vibrations below. Clicking on a peak will take you to corresponding vibration.

These vibrations are the result of a C++ program. For an explanation of how it works, click here.
This is a CO2 molecule vibrating symetrically. The vibration does not create a dipole moment and therfore does not show up on the IR spectrum.

This is a CO2 molecule vibrating asymetircally.

This is a CO2 molecule bending.

This is also a CO2 molecule bending. It is rotated 90 from the other bending one, and therefore degenerate.

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