Absorption Spectrum

We know that light is electromagnetic radiation composed of several frequencies of radiation. An ordinary light features a wide range of wavelengths with respective frequencies. Electromagnetic waves can travel in a vacuum at the speed of light. The electromagnetic spectrum consists of a span of all electromagnetic radiation which further contains many subranges which are commonly referred to as portions. Microwaves, infrared light, ultraviolet light, X-rays and gamma-rays are types of radiation included in the electromagnetic spectrum.

When the white light is passed through a medium, they get split according to their respective frequencies and wavelengths. The white light spectrum starts from 7.5 x 10¹⁴ Hz for the violet colour to 4 x 10¹⁴ Hz for the red colour. The interaction of electromagnetic radiation with matter causes the molecules and atoms present in a matter to absorb energy and reach a higher energy state. This higher energy state is unstable, and hence they have to emit energy in the form of radiations to return to their original states. This process generates emission spectra and absorption spectra.

Let us know more about spectra and various types, along with their applications.

Table of Content

• Spectra and Spectroscopy
• Spectra classification
• Emission Spectra
• Emission Spectrum Classification
• Absorption Spectra
• Absorption Spectroscopy
• Absorption Spectroscopy Applications
• Frequently Asked Questions – FAQs

Spectra and Spectroscopy

The plural form of spectrum is a spectra. Spectrum is widely used in the field of optics and many more fields. Spectrum features a wide range of wavelengths of different frequency radiations. A rainbow is a spectrum that constitutes different wavelengths of light. The spectrum of light from the rainbow is commonly referred to as VIBGYOR. The prism is also an ideal example to describe the spectrum of radiation. When the white light passes through the prism, it gets separated into different wavelengths of light known as the spectrum.

The instrument used to separate the radiations of different wavelengths is known as Spectroscope or Spectrograph. A spectrometer is a scientific device that aids to separate and measure spectral components of a physical phenomenon. Branch of science that deals with the study of the spectrum are known as spectroscopy.

A spectrograph features a prism or diffraction grating that is used to disperse light. The emerging light after the dispersion from the prism is examined using a photographic film.

Classification of Spectra

Spectra is classified into two types:

• Emission spectra
• Absorption spectra

Click the below video for understanding the definition and the types of spectrum:

Emission Spectra

The spectrum formed by the radiation emitted by electrons in the excited molecules or atoms is known as the emission spectrum. The emission spectrum comprises frequencies of electromagnetic radiation due to the influence of chemical elements or chemical compounds emitted due to an atom or molecule, making the transition from a high energy state to a lower energy state. These excited electrons have to radiate energy to return to ground states from the excited state, which is unstable. The frequencies of these emitted light form the emission spectrum.

Classification of Emission Spectra

Based on the source, the emission spectrum is classified into two types:

• Continuous spectrum: When the spectrum has no breaks or gaps between the wavelength range is known as a continuous spectrum. A rainbow is an example of a continuous spectrum.
• Line spectrum: When the spectrum has a discrete line that can be categorized as excited atoms is known as a line spectrum. Hydrogen produces a line spectrum.

Absorption Spectra

This spectrum is constituted by the frequencies of light transmitted with dark bands when the electrons absorb energy in the ground state to reach higher energy states. This type of spectrum is produced when atoms absorb energy. Let’s know how absorption spectra are formed.

When light from any source is passed through the solution or vapour, a pattern comprising dark lines is obtained. This pattern is analysed using the spectroscope. Depending on the nature of the chemical or element, certain radiation is absorbed by the chemical or element when passed through it.

The dark line pattern is seen exactly in the same place where coloured lines are seen in the emission spectrum. The spectrum thus obtained is known as the absorption spectrum.

Emission spectra can emit all the colours in an electromagnetic spectrum, while the absorption spectrum can have a few colours missing due to the redirection of absorbed photons. The wavelengths of light absorbed help figure out the number of substances in the sample.

The pattern of absorption lines, emission lines, and the continuous spectrum is shown below.

Read more about the emission spectrum.

What is Absorption Spectroscopy?

Absorption spectroscopy is a spectroscopic technique that is used for measuring the absorption of radiation as it interacts with the sample. The radiation could be a function of either frequency or wavelength.

Absorption spectroscopy is related to the absorption spectrum because the sample used interacts with photons from the radiating field. The intensity of the absorption differs depending on the frequency and this variation is the absorption spectrum.

Applications Absorption Spectroscopy

Chemical Analysis

The specificity and the quantitative nature of absorption spectroscopy make it an ideal choice for chemical analysis. The absorption spectrum of the compounds can be distinguished from one another using absorption spectroscopy. This is possible because of the specificity of the absorption spectrum. It is also used for determining the unknown samples from the given mixture.
An infrared gas analyser is an application of absorption spectroscopy used to identify the presence of pollutants in the air. It helps in differentiating between the pollutants from nitrogen, oxygen, water, and other constituents.

Remote Sensing

In remote sensing, absorption spectroscopy is used for analytical purposes such as measuring the presence of hazardous elements without bringing the sample in contact with the instrument.

Stay tuned with BYJU’S for more such interesting articles on atomic spectra, emission spectra and electromagnetic waves in detail.