The principle of infrared (IR) spectroscopy is based on the fact that molecules absorb infrared radiation at specific frequencies that cause their chemical bonds to vibrate.
Here’s a detailed explanation:
- Molecular vibrations:
- Atoms in a molecule are bonded together and can vibrate in different ways: stretching (bond length changes) or bending (bond angle changes).
- Each type of bond (C–H, O–H, C=O, etc.) vibrates at a characteristic frequency.
- Absorption of IR radiation:
- When a molecule is exposed to infrared radiation, it absorbs energy only if the frequency of the IR light matches the natural vibration frequency of a bond.
- This absorption causes an increase in vibrational energy.
- Detection:
- The IR spectrometer measures how much IR radiation is absorbed at each frequency and produces a spectrum.
- The spectrum shows peaks corresponding to different functional groups in the molecule.
- Interpretation:
- Each peak in the IR spectrum represents a specific bond vibration.
- By analyzing the positions and intensities of these peaks, we can identify functional groups and infer aspects of the molecular structure.
In short:
IR spectroscopy works on the principle that molecules absorb infrared light at specific frequencies corresponding to the vibrations of their chemical bonds, allowing identification of functional groups.