Infrared (IR) spectrophotometry is a technique used to study molecular vibrations and identify functional groups in a molecule.
Here’s how it works:
1. IR Light Source
- The instrument shines infrared light onto the sample.
- IR light has longer wavelengths than visible light, which match the energies needed to make chemical bonds vibrate.
2. Absorption by Molecules
- Molecules absorb specific IR wavelengths depending on the types of bonds and atoms.
- Each functional group (like -OH, -NH, C=O) absorbs IR light at a characteristic wavelength.
3. Transmission or Reflection
- Some IR light passes through the sample (transmitted) or bounces off (reflected).
- The instrument measures how much light is absorbed at each wavelength.
4. Detector
- The detector records the amount of light absorbed at different wavelengths.
- This data is converted into a spectrum.
5. IR Spectrum
- The x-axis shows wavenumber (cm⁻¹), related to frequency of vibration.
- The y-axis shows absorbance or transmittance.
- Peaks correspond to specific bond vibrations, helping identify functional groups.
In short:
IR spectrophotometry works by shining infrared light on a sample, measuring which wavelengths are absorbed by molecular vibrations, and producing a spectrum that reveals the functional groups present in the molecule.