Understanding the Interaction between Light and Matter

Spectroscopy is one of the most studied topics in today’s research on quantum mechanics. There are many unexplored areas in quantum mechanics that are being studied by chemists to understand how light fields interact with matter. The light-matter interactions are a result of an oscillating electromagnetic field that can interact with charged particles.

The chemists study how electromagnetic radiation of any form can interact with atoms and molecules. This interaction is called spectroscopy. Based on the type of electromagnetic radiation, the nature of spectroscopy also varies.

Different types of spectroscopy give us different perspectives. The interpretation of spectroscopy requires a model, whether it is stated or not. Spectroscopy requires both modeling and laboratory practice to be useful to distinguish between different electromagnetic radiations. This study can determine the underlying process of the interaction of light and matter.

UV-Vis spectroscopy

UV-Vis spectroscopy

Different phenomenons can take place depending on the energy of a photon that is absorbed or emitted by a matter. One example of such a phenomenon when a hydrogen atom absorbs light in a UV region of the electromagnetic spectrum. When an atom absorbs a UV photon from visible light, the photon’s energy can excite one of the atom’s electron to a level higher. This excitation of the electron in an atom is known as transition. In order for the transition to occur, the energy of the photon should be higher than or at least equal to the difference in energy between the two energy levels. However, after excitation, the electron becomes more unstable and will quickly fall back to the lower energy level. By doing so, it will emit a photon with the energy equivalent to the difference between the higher and lower level of energy of the electron.

When the transition between the energy level is large, more energy will be absorbed/emitted by the transition. Larger energy transitions have higher frequency photos associated with them. When an electron falls from the third to second energy level, it emits a photon of red light. Similarly, when it falls from the sixth energy level to the second energy level forming a larger transition, it emits a purple light photon. Purple light photon has a higher frequency than red light.

The energy transition for electrons of different matters will always be unique. This helps the chemists to identify the elements based on their emission spectrum. The emission spectrum of each element can be as unique as fingerprints.


Infrared(IR) spectroscopy

The lower energy radiations in the infrared regions of the spectrum can produce the same kinds of changes withing atoms like UV radiation. This radiation may not have enough energy to excite electrons but will cause the chemical bonds within molecules to vibrate in different ways. The chemists have special labs to study the IR absorption spectrum for a molecule, which can determine what kind of chemical bonds are present in a molecule.

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