IR spectroscopy

In a nutshell

Infrared (IR) spectroscopy is an analytical technique which is used to identify a compound. Each bond has a unique vibration when exposed to IR, and this can be used to deduce functional groups present in a molecule. Molecules have a unique section of their spectra, called a fingerprint region which can identify the exact molecule present.

What is infrared spectroscopy?

Infrared (IR) spectroscopy can be used to identify compounds in a sample. The principles of IR are based on the vibrations of atoms. Atoms are joined by a chemical bond that is always vibrating. When exposed to the infrared region of the electromagnetic spectrum, every bond has a unique frequency that it vibrates.

The IR spectrometer

Infrared radiation is passed through a sample and the bond absorbs energy from the radiation and vibrates more. The bond will absorb radiation that has the same frequency as its natural frequency. This means that the radiation emerging from the sample will be missing the frequencies of the bonds that are present, hence the emerging spectra will show the bonds present.

Infrared spectra

The infrared spectrometer will plot a graph called an IR spectrum. This graph shows the transmittance (intensity of radiation) against the frequency of radiation. The frequency of radiation is shown as a wavenumber ( $cm^{-1}$ ).