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What is Spectroscopy?

Spectroscopy includes all the analytical processes which are based on the interaction of electromagnetic waves and matter. When energy is transmitted, there occurs an interaction between electromagnetic radiation (e.g. photons) and matter. This can be observed, for example, when an atom becomes excited. A photon’s energy is directly proportional to its frequency.

The following holds:

Δ E = h ⋅ ν

In this case, h is Planck’s Constant, ν is the wavelength frequency of the photon and Δ E the energy differential. This equation is known as the fundamental equation of spectroscopy. It means that the amount of energy of a photon with a defined wavelength is known. This amount is known as a discrete energy state. The electrons in atoms also adopt discrete energy states. If a photon collides with an electron at rest, it only releases its energy if it pushes the electron into a permitted energy state. The photon must release all of its energy. After it releases its energy, it no longerexists. After absorbing the photon’s energy, the electron jumps to a higher energy level. The excited electron “seeks“ to return to the lowest energy value, that is, to return to its ground state. In order to do this, it must release its energy. This can happen in various ways.

For example, the electron can transform a part of the energy into kinetic energy, e.g. the vibration of the lattice in a crystal. The electron then has a lower energy value than it did just after it was excited. If the electron is then at an energy level from which the remaining additional energy can be emitted as radiation, the emitted photon has less energy than the absorbed photon. The wavelength of the emitted particle has been shifted to longer wavelengths energy than the absorbed photon. If the electron emits the energy as heat, the absorbed energy is transformed into long-wave radiation which can no longer be detected by a spectrometer. We observe the radiation as having been absorbed. Electromagnetic waves exist on a frequency spectrum of which we can perceive only a very small part. Each element or molecule behaves in its own unique way when it interacts with electromagnetic waves. So every sample has its own specific spectral “fingerprint“. For most applications it is quite sufficient to observe either a small range of the spectrum or certain discrete wavelengths.