Spectral analysis

Dark lines on spectral stripes were noticed long ago (for example, Wollaston noted them), but the first serious study of these lines was undertaken only in 1814 by Joseph Fraunhofer . In his honor, the effect was called the Fraunhofer Lines . Fraunhofer established the stability of the position of the lines, compiled a table of them (he counted 574 lines in total), assigned an alphanumeric code to each. No less important was his conclusion that the lines are not connected either with optical material or with the earth's atmosphere, but are a natural characteristic of sunlight. He found similar lines in artificial light sources, as well as in the spectra of Venus and Sirius .

It soon became clear that one of the most distinct lines always appears in the presence of sodium . In 1859, G. Kirchhoff and R. Bunsen, after a series of experiments, concluded: each chemical element has its own unique linear spectrum, and from the spectrum of celestial bodies we can draw conclusions about the composition of their substance. From that moment on, spectral analysis appeared in science, a powerful method for the remote determination of chemical composition.

To test the method in 1868, the Paris Academy of Sciences organized an expedition to India, where a total solar eclipse was coming. There, scientists discovered: all the dark lines at the time of the eclipse, when the radiation spectrum changed the absorption spectrum of the solar corona , became, as was predicted, bright against a dark background.

The nature of each of the lines, their relationship with chemical elements was clarified gradually. In 1860, Kirchhoff and Bunsen discovered cesium using spectral analysis, and rubidium in 1861. Also in 1861, William Crookes discovered spectral analysis of thallium . And helium was discovered on the Sun 27 years earlier than on Earth (1868 and 1895, respectively).

In 1933, the Leningrad Institute of Historical Technology first applied spectral analysis of ancient metal products ^[1] .

The atoms of each chemical element have strictly defined resonant frequencies, as a result of which they emit or absorb light at these frequencies.

Dark lines appear when electrons located at the lower energy levels of an atom, under the influence of radiation from a light source, instantly rise to a higher level, absorbing light waves of a certain length, and immediately after that fall back to the previous level, emitting waves of the same length vice versa - but since this radiation is scattered evenly in all directions, in contrast to the directional radiation from the initial source, dark lines in the place / places are visible on the spectrogram on the spectra, respectively at a given length / wavelengths. These wavelengths differ for each substance and are determined by the difference in energy between the electronic energy levels in the atoms of this substance.

The number of such lines for a particular substance is equal to the number of possible singular variants of electron transitions between energy levels; for example, if the electrons in the atoms of a particular substance are located on two levels, there is only one possible transition - from the internal level to the external (and vice versa), and there will be two dark lines on the spectrogram for this substance. If there are three electronic energy levels, then there are already three possible transition options (1-2, 2-3, 1-3), and there will also be three dark lines in the spectrogram.

The intensity of the lines depends on the amount of substance and its condition. In the quantitative spectral analysis, the content of the test substance is determined by the relative or absolute intensities of the lines or bands in the spectra.

Optical spectral analysis is characterized by relative simplicity of execution, the absence of complex preparation of samples for analysis, and a small amount of the substance needed for analysis (within 10-30 mg).

Atomic spectra (absorption or emission) are obtained by converting a substance into a vapor state by heating the sample to 1000-10000 ° C. As sources of excitation of atoms in the emission analysis of conductive materials, a spark, an alternating current arc are used; while the sample is placed in the crater of one of the carbon electrodes. For the analysis of solutions, flame or plasma of various gases is widely used.

Recently, emission and mass spectrometric methods of spectral analysis based on the excitation of atoms and their ionization in argon plasma of induction discharges, as well as in a laser spark, have become most widespread.

Spectral analysis is a sensitive method and is widely used in analytical chemistry, astrophysics, metallurgy, mechanical engineering, geological exploration, archeology and other branches of science.

In the theory of signal processing, spectral analysis means analyzing the distribution of the energy of a signal (e.g., sound) over frequencies, wave numbers, etc.

• Spectroscopy
• Fourier Transform
• Correlation

• Spectroscopy links in the Open Directory Project link directory (dmoz)
• Amateur spectroscopy links in the Open Directory Project (dmoz)
• Database of spectra of all chemical elements (tables)
• MIT Spectroscopy Lab's History of Spectroscopy
• Timeline of spectroscopy
• NIST government spectroscopy data