A Guide to Molecular Spectroscopy

By  //  January 7, 2022

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Physics is a branch of science with numerous theories and explanations of everything in the form of formulae or, sometimes, massive explanations of theories. Spectroscopy is one of the many parts of physics that is complicated to understand but important in many ways.

As many of us might know, spectroscopy studies communication between matter and electromagnetic radiation as a function of wavelength. When we talk about spectroscopy, it has many types, one of which is molecular spectroscopy.

It studies the measurements of communication between electromagnetic waves and matter. It is used to produce an absorption spectrum from which structural and compositional information is deduced.

 Types of Molecular Spectra

There are three types of molecular spectra:

1) Pure Rotational Spectra

2) Vibrational Rotational Spectra

3) Electronic Band Spectra

Let’s read on to know more about these types in depth.

1) Pure Rotational Spectra:

As the name suggests, rotational spectra mean when the lower amount of energy absorbs molecules. It makes the transition from one rotational level to another rotational level in the same vibrational level as before. You can observe rotational spectra from spectral regions of far infrared and microwaves.

Moreover, energies between spectral regions are very dwarfish(micro); thus, another name of rotational spectra can be known as microwave spectra. Molecules like HF and HCI have pure rotational spectra.

Molecular spectroscopy is also concerned with the measurements of energies between the quantized rotational stage of the molecules in the gas phase. Thus it is called pure rotational spectra.

2) Vibrational Rotational Spectra:

As per the above information, rotational spectra are related to vibrational spectra and vibrational, rotational spectra are related to the electronic level of molecules. In vibrational, rotational spectra, when molecules absorb enough energy, it creates a transition of molecules from one vibrational level to another vibrational level within the same electronic level.

As we can see, Rotational transitions and Vibrational transitions take place to obtain vibrational, rotational spectra. As the name suggests, Vibrational, rotational spectra are a combination of Rotational and vibrational transitions. You can observe vibrational, rotational spectra in near-infrared spectral regions, which is observable to all of us in infrared spectra.

3) Electronic Band Spectra:
Electro band spectra are a bit different yet related to both vibrational spectra and rotational spectra. It means that when the energy of radiation is large enough, it causes the transition of molecules from one electronic level to another.

Also, this transition is followed by both vibrational level and rotational level changes, and for each vibrational transition, a set of lines that are closely spaced appears. These closely spaced lines are also called bands, and because of corresponding rotational changes, it is called electro band spectra. As we can see, all of these three types of molecular spectroscopy are interrelated to each other in one way or another.

 Instruments and Applications:

Molecular spectroscopy is used in many ways like pharmaceuticals industries, life sciences, combinatorial chemistry, etc. Many industries manufacture molecular spectroscopy instruments for labs to measure UV, fluorescence, and infrared.

The Agilent Molecular Spectroscopy instrument portfolio has the best in use instruments that are developed in capabilities and breadth. These instruments also include best innovations like carrying 3500 UV-Vis and laser direct infrared chemical imaging. These spectroscopy systems are most capable of providing you with the right solution for your challenges. 


When we talk about advancements in molecular spectroscopy, we can include how it has advanced in the field of biology, chemicals, and sensing applications.

Although these advancements resulted from the development of other new techniques in the field of Raman, infrared, and fluorescence spectroscopy, we can say molecular spectroscopy has developed in many ways because we can see how these techniques have moved beyond their limitations in many ways.

But the downside of it is this work is carried out more in academic settings, but we can hope that these advancements in Spectroscopy can be beneficial for industries.

There is still much research going on in the field of spectroscopy, and molecular spectroscopy is one of the fields that has developed more in the last few years. Molecular spectroscopy may be unknown to some industries, but most industries have benefited from it.