Abstract: Application of spectral analysis. School encyclopedia

Emission spectra. The spectral composition of radiation for different substances has a very diverse character. However, all spectra are divided into three types: a) continuous spectrum; b) line spectrum; c) striped spectrum.

A) Continuous spectrum. Heated solid and liquid bodies and gases (at high pressure) emit light, the decomposition of which gives a continuous spectrum in which spectral colors continuously transform into one another. The nature of the continuous spectrum and the very fact of its existence are determined not only by the properties of individual emitting atoms, but also by the interaction of atoms with each other. Continuous spectra are the same for different substances and therefore cannot be used to determine the composition of a substance.

b) Line (atomic) spectrum. Excited atoms of rarefied gases or vapors emit light, the decomposition of which gives a line spectrum consisting of individual colored lines. Each chemical element has a characteristic line spectrum. The atoms of such substances do not interact with each other and emit light only at certain wavelengths. Isolated atoms of a given chemical element emit strictly defined wavelengths. This allows us to judge the chemical composition of the light source from the spectral lines.

V) Molecular (banded) spectrum The spectrum of a molecule consists of a large number of individual lines, merging into stripes, clear at one end and blurry at the other. Unlike line spectra, striped spectra are created not by atoms, but by molecules that are not bound or weakly bound to each other. Series of very close lines are grouped in separate parts of the spectrum and fill entire bands. In 1860, German scientists G. Kirchhoff and R. Bunsen, studying the spectra of metals, established the following facts:

1) each metal has its own spectrum;

2) the spectrum of each metal is strictly constant;

3) the introduction of any salt of the same metal into the burner flame always leads to the appearance of the same spectrum;

4) when a mixture of salts of several metals is introduced into the flame, all their lines simultaneously appear in the spectrum;

5) the brightness of the spectral lines depends on the concentration of the element in a given substance.

Absorption spectra. If white light from a source producing a continuous spectrum is passed through the vapor of the substance under study and then decomposed into a spectrum, then against the background of the continuous spectrum dark absorption lines are observed in the same places where the lines of the emission spectrum of the vapor of the element under study would be located. Such spectra are called atomic absorption spectra.

All substances whose atoms are in an excited state emit light waves, the energy of which is distributed in a certain way over wavelengths. The absorption of light by a substance also depends on the wavelength. Atoms absorb radiation only at those wavelengths that they can emit at a given temperature.

Spectral analysis. The phenomenon of dispersion is used in science and technology in the form of a method for determining the composition of a substance, called spectral analysis. This method is based on the study of light emitted or absorbed by a substance. Spectral analysis is a method of studying the chemical composition of a substance based on the study of its spectra.

Spectral devices. Spectral apparatus is used to obtain and study spectra. The simplest spectral devices are a prism and a diffraction grating. More accurate ones are a spectroscope and a spectrograph.

Spectroscope is a device that is used to visually examine the spectral composition of light emitted by a certain source. If the spectrum is recorded on a photographic plate, then the device is called spectrograph.

Application of spectral analysis. Line spectra play a particularly important role because their structure is directly related to the structure of the atom. After all, these spectra are created by atoms that do not experience external influences. The composition of complex, mainly organic mixtures is analyzed by their molecular spectra.

Using spectral analysis, it is possible to detect a given element in the composition of a complex substance, even if its mass does not exceed 10 -10 g. The lines inherent in a given element make it possible to qualitatively judge its presence. The brightness of the lines makes it possible (subject to standard excitation conditions) to quantitatively judge the presence of a particular element.

Spectral analysis can also be carried out using absorption spectra. In astrophysics, many physical characteristics of objects can be determined from spectra: temperature, pressure, speed of movement, magnetic induction, etc. Using spectral analysis, the chemical composition of ores and minerals is determined.

The main areas of application of spectral analysis are: physical and chemical research; mechanical engineering, metallurgy; nuclear industry; astronomy, astrophysics; forensics.

Modern technologies for creating the latest building materials (metal-plastic, plastic) are directly interconnected with such fundamental sciences as chemistry and physics. These sciences use modern methods of studying substances. Therefore, spectral analysis can be used to determine the chemical composition of building materials from their spectra.

Spectral analysis

Spectral analysis- a set of methods for qualitative and quantitative determination of the composition of an object, based on the study of the spectra of interaction of matter with radiation, including the spectra of electromagnetic radiation, acoustic waves, distribution of masses and energies of elementary particles, etc.

Depending on the purposes of analysis and the types of spectra, several methods of spectral analysis are distinguished. Atomic And molecular spectral analyzes make it possible to determine the elemental and molecular composition of a substance, respectively. In the emission and absorption methods, the composition is determined from the emission and absorption spectra.

Mass spectrometric analysis is carried out using the mass spectra of atomic or molecular ions and allows one to determine the isotopic composition of an object.

Story

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

It soon became clear that one of the clearest lines always appeared 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 line spectrum, and from the spectrum of celestial bodies one can draw conclusions about the composition of their substance. From this moment on, spectral analysis appeared in science, a powerful method for 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 moment of the eclipse, when the emission spectrum replaced the absorption spectrum of the solar corona, became, as predicted, bright against a dark background.

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

Principle of operation

The atoms of each chemical element have strictly defined resonant frequencies, as a result of which it is at these frequencies that they emit or absorb light. This leads to the fact that in a spectroscope, lines (dark or light) are visible on the spectra in certain places characteristic of each substance. The intensity of the lines depends on the amount of substance and its state. In quantitative spectral analysis, the content of the substance under study is determined by the relative or absolute intensities of lines or bands in the spectra.

Optical spectral analysis is characterized by relative ease of implementation, the absence of complex sample preparation for analysis, and a small amount of substance (10-30 mg) required for analysis of a large number of elements.

Atomic spectra (absorption or emission) are obtained by transferring the substance into a vapor state by heating the sample to 1000-10000 °C. A spark or an alternating current arc are used as sources of excitation of atoms in the emission analysis of conductive materials; in this case, the sample is placed in the crater of one of the carbon electrodes. Flames or plasmas of various gases are widely used to analyze solutions.

Application

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 and other branches of science.

In signal processing theory, spectral analysis also means the analysis of the energy distribution of a signal (for example, audio) over frequencies, wave numbers, etc.

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Spectral analysis- The content of the article. I. Glow of bodies. Emission spectrum. Solar spectrum. Fraunhofer lines. Prismatic and diffraction spectra. Color scattering of prism and grating. II. Spectroscopes. Elbowed and straight spectroscope à vision directe.… … Encyclopedic Dictionary F.A. Brockhaus and I.A. Efron

Introduction……………………………………………………………………………….2

Radiation mechanism………………………………………………………………………………..3

Energy distribution in the spectrum……………………………………………………….4

Types of spectra……………………………………………………………………………………….6

Types of spectral analyzes………………………………………………………7

Conclusion………………………………………………………………………………..9

Literature……………………………………………………………………………….11

Introduction

Spectrum is the decomposition of light into its component parts, rays of different colors.

The method of studying the chemical composition of various substances from their line emission or absorption spectra is called spectral analysis. A negligible amount of substance is required for spectral analysis. Its speed and sensitivity have made this method indispensable both in laboratories and in astrophysics. Since each chemical element of the periodic table emits a line emission and absorption spectrum characteristic only for it, this makes it possible to study the chemical composition of the substance. The physicists Kirchhoff and Bunsen first tried to make it in 1859, building spectroscope. Light was passed into it through a narrow slit cut from one edge of the telescope (this pipe with a slit is called a collimator). From the collimator, the rays fell onto a prism covered with a box lined with black paper on the inside. The prism deflected the rays that came from the slit. The result was a spectrum. After that, they covered the window with a curtain and placed a lit burner at the collimator slit. Pieces of various substances were introduced alternately into the candle flame, and they looked through a second telescope at the resulting spectrum. It turned out that the incandescent vapors of each element produced rays of a strictly defined color, and the prism deflected these rays to a strictly defined place, and therefore no one color could mask the other. This led to the conclusion that a radically new method of chemical analysis had been found - using the spectrum of a substance. In 1861, based on this discovery, Kirchhoff proved the presence of a number of elements in the chromosphere of the Sun, laying the foundation for astrophysics.

Radiation mechanism

The light source must consume energy. Light is electromagnetic waves with a wavelength of 4*10 -7 - 8*10 -7 m. Electromagnetic waves are emitted by the accelerated movement of charged particles. These charged particles are part of atoms. But without knowing how the atom is structured, nothing reliable can be said about the radiation mechanism. It is only clear that there is no light inside an atom, just as there is no sound in a piano string. Like a string that begins to sound only after being struck by a hammer, atoms give birth to light only after they are excited.

In order for an atom to begin to radiate, energy must be transferred to it. When emitting, an atom loses the energy it receives, and for the continuous glow of a substance, an influx of energy to its atoms from the outside is necessary.

Thermal radiation. The simplest and most common type of radiation is thermal radiation, in which the energy lost by atoms to emit light is compensated by the energy of thermal motion of atoms or (molecules) of the emitting body. The higher the body temperature, the faster the atoms move. When fast atoms (molecules) collide with each other, part of their kinetic energy is converted into excitation energy of the atoms, which then emit light.

The thermal source of radiation is the Sun, as well as an ordinary incandescent lamp. The lamp is a very convenient, but low-cost source. Only about 12% of the total energy released by electric current in a lamp is converted into light energy. The thermal source of light is a flame. Grains of soot heat up due to the energy released during fuel combustion and emit light.

Electroluminescence. The energy needed by atoms to emit light can also come from non-thermal sources. During a discharge in gases, the electric field imparts greater kinetic energy to the electrons. Fast electrons experience collisions with atoms. Part of the kinetic energy of electrons goes to excite atoms. Excited atoms release energy in the form of light waves. Due to this, the discharge in the gas is accompanied by a glow. This is electroluminescence.

Cathodoluminescence. The glow of solids caused by the bombardment of electrons is called cathodoluminescence. Thanks to cathodoluminescence, the screens of cathode ray tubes of televisions glow.

Chemiluminescence. In some chemical reactions that release energy, part of this energy is directly spent on the emission of light. The light source remains cool (it is at ambient temperature). This phenomenon is called chemioluminescence.

Photoluminescence. Light incident on a substance is partially reflected and partially absorbed. The energy of absorbed light in most cases only causes heating of bodies. However, some bodies themselves begin to glow directly under the influence of radiation incident on them. This is photoluminescence. Light excites the atoms of a substance (increases their internal energy), after which they are illuminated themselves. For example, the luminous paints that cover many Christmas tree decorations emit light after being irradiated.

The light emitted during photoluminescence, as a rule, has a longer wavelength than the light that excites the glow. This can be observed experimentally. If you direct a light beam at a vessel containing fluoresceite (an organic dye),

passed through a violet light filter, this liquid begins to glow with green-yellow light, i.e. light of a longer wavelength than violet light.

The phenomenon of photoluminescence is widely used in fluorescent lamps. Soviet physicist S.I. Vavilov proposed covering the inner surface of the discharge tube with substances capable of glowing brightly under the action of short-wave radiation from a gas discharge. Fluorescent lamps are approximately three to four times more economical than conventional incandescent lamps.

The main types of radiation and the sources that create them are listed. The most common sources of radiation are thermal.

Energy distribution in the spectrum

On the screen behind the refractive prism, monochromatic colors in the spectrum are arranged in the following order: red (which has the longest wavelength among visible light waves (k = 7.6 (10-7 m and the smallest refractive index), orange, yellow, green, cyan, blue and violet (having the shortest wavelength in the visible spectrum (f = 4 (10-7 m and the highest refractive index). None of the sources produces monochromatic light, that is, light of a strictly defined wavelength. Experiments on decomposition of light into a spectrum using a prism, as well as experiments on interference and diffraction.

The energy that light carries with it from the source is distributed in a certain way over the waves of all lengths that make up the light beam. We can also say that energy is distributed over frequencies, since there is a simple relationship between wavelength and frequency: v = c.

The flux density of electromagnetic radiation, or intensity /, is determined by the energy &W attributable to all frequencies. To characterize the frequency distribution of radiation, it is necessary to introduce a new quantity: the intensity per unit frequency interval. This quantity is called the spectral density of radiation intensity.

The spectral radiation flux density can be found experimentally. To do this, you need to use a prism to obtain the radiation spectrum, for example, of an electric arc, and measure the radiation flux density falling on small spectral intervals of width Av.

You cannot rely on your eye to estimate energy distribution. The eye has selective sensitivity to light: its maximum sensitivity lies in the yellow-green region of the spectrum. It is best to take advantage of the property of a black body to almost completely absorb light of all wavelengths. In this case, radiation energy (i.e. light) causes heating of the body. Therefore, it is enough to measure the body temperature and use it to judge the amount of energy absorbed per unit time.

An ordinary thermometer is too sensitive to be successfully used in such experiments. More sensitive instruments are needed to measure temperature. You can take an electric thermometer, in which the sensitive element is made in the form of a thin metal plate. This plate must be coated with a thin layer of soot, which almost completely absorbs light of any wavelength.

The heat-sensitive plate of the device should be placed in one or another place in the spectrum. The entire visible spectrum of length l from red to violet rays corresponds to the frequency interval from v cr to y f. The width corresponds to a small interval Av. By heating the black plate of the device, one can judge the radiation flux density per frequency interval Av. Moving the plate along the spectrum, we will find that most of the energy is in the red part of the spectrum, and not in the yellow-green, as it seems to the eye.

Based on the results of these experiments, it is possible to construct a curve of the dependence of the spectral density of radiation intensity on frequency. The spectral density of radiation intensity is determined by the temperature of the plate, and the frequency is not difficult to find if the device used to decompose the light is calibrated, that is, if it is known what frequency a given part of the spectrum corresponds to.

By plotting along the abscissa axis the values of the frequencies corresponding to the midpoints of the intervals Av, and along the ordinate axis the spectral density of the radiation intensity, we obtain a number of points through which we can draw a smooth curve. This curve gives a visual representation of the distribution of energy and the visible part of the spectrum of the electric arc.

One of the main methods for analyzing the chemical composition of a substance is spectral analysis. An analysis of its composition is carried out based on the study of its spectrum. Spectral analysis - used in various studies. With its help, a complex of chemical elements was discovered: He, Ga, Cs. in the atmosphere of the Sun. As well as Rb, In and XI, the composition of the Sun and most other celestial bodies is determined.

Applications

Spectral expertise, common in:

Metallurgy;
Geology;
Chemistry;
Mineralogy;
Astrophysics;
Biology;
medicine, etc.

Allows you to find the smallest amounts of an established substance in the objects being studied (up to 10 - MS). Spectral analysis is divided into qualitative and quantitative.

Methods

The method of establishing the chemical composition of a substance based on the spectrum is the basis of spectral analysis. Line spectra have a unique personality, just like human fingerprints or the pattern of snowflakes. The uniqueness of patterns on the skin of a finger is a great advantage for searching for a criminal. Therefore, thanks to the peculiarities of each spectrum, it is possible to establish the chemical content of the body by analyzing the chemical composition of the substance. Even if its mass of an element does not exceed 10 - 10 g, using spectral analysis it can be detected in the composition of a complex substance. This is a fairly sensitive method.

Emission spectral analysis

Emission spectral analysis is a series of methods for determining the chemical composition of a substance from its emission spectrum. The basis for the method of establishing the chemical composition of a substance - spectral examination - is based on the patterns in the emission spectra and absorption spectra. This method allows you to identify millionths of a milligram of a substance.

There are methods of qualitative and quantitative examination, in accordance with the establishment of analytical chemistry as a subject, the purpose of which is to formulate methods for establishing the chemical composition of a substance. Methods for identifying a substance become extremely important within qualitative organic analysis.

Based on the line spectrum of vapors of any substance, it is possible to determine which chemical elements are contained in its composition, because any chemical element has its own specific emission spectrum. This method of establishing the chemical composition of a substance is called qualitative spectral analysis.

X-ray spectral analysis

There is another method for identifying a chemical called X-ray spectral analysis. X-ray spectral analysis is based on the activation of the atoms of a substance when it is irradiated with X-rays, a process called secondary or fluorescent. Activation is also possible when irradiated with high-energy electrons; in this case, the process is called direct excitation. As a result of the movement of electrons in the deeper inner electron layers, X-ray lines appear.

The Wulff-Bragg formula allows you to set the wavelengths in the composition of X-ray radiation when using a crystal of a popular structure with a known distance d. This is the basis of the determination method. The substance being studied is bombarded with high-speed electrons. It is placed, for example, on the anode of a dismountable X-ray tube, after which it emits characteristic X-rays that fall on a crystal of a known structure. The angles are measured and the corresponding wavelengths are calculated using the formula, after photographing the resulting diffraction pattern.

Techniques

Currently, all methods of chemical analysis are based on two techniques. Either at the physical test, or at the chemical test, comparing the established concentration with its unit of measurement:

Physical

The physical technique is based on the method of correlating a unit of quantity of a component with a standard by measuring its physical property, which depends on its content in a sample of the substance. The functional relationship “Property saturation – component content in the sample” is determined by trial by calibrating the means for measuring a given physical property according to the component being installed. From the calibration graph, quantitative relationships are obtained, constructed in the coordinates: “saturation of a physical property - concentration of the installed component.”

Chemical

A chemical technique is used in the method of correlating a unit of quantity of a component with a standard. Here the laws of conservation of the quantity or mass of a component during chemical interactions are used. Chemical interactions are based on the chemical properties of chemical compounds. In a sample of a substance, a chemical reaction is carried out that meets the specified requirements to determine the desired component, and the volume or mass involved in the specific chemical reaction of the components is measured. Quantitative relationships are obtained, then the number of equivalents of a component for a given chemical reaction or the law of conservation of mass is written down.

Devices

Instruments for analyzing the physical and chemical composition of a substance are:

Gas analyzers;
Alarms for maximum permissible and explosive concentrations of vapors and gases;
Concentrators for liquid solutions;
Density meters;
Salt meters;
Moisture meters and other devices similar in purpose and completeness.

Over time, the range of analyzed objects increases and the speed and accuracy of the analysis increases. One of the most important instrumental methods for establishing the atomic chemical composition of a substance is spectral analysis.

Every year more and more complexes of instruments appear for quantitative spectral analysis. They also produce the most advanced types of equipment and methods for spectrum recording. Spectral laboratories are organized initially in mechanical engineering, metallurgy, and then in other areas of industry. Over time, the speed and accuracy of the analysis increases. In addition, the area of analyzed objects is expanding. One of the main instrumental methods for determining the atomic chemical composition of a substance is spectral analysis.

Spectral analysis is one of the most important physical methods for studying substances. Designed to determine the qualitative and quantitative composition of a substance based on its spectrum.

Chemists have long known that compounds of certain chemical elements, if added to a flame, give it characteristic colors. Thus, sodium salts make the flame yellow, and boron compounds make it green. The color of a substance occurs when it either emits waves of a certain length or absorbs them from the full spectrum of white light incident on it. In the second case, the color visible to the eye turns out to correspond not to these absorbed waves, but to others - additional ones, which, when added to them, give white light.

These patterns, established at the beginning of the last century, were generalized in 1859-1861. German scientists G. Kirchhoff and R. Bunsen, who proved that each chemical element has its own characteristic spectrum. This made it possible to create a type of elemental analysis - atomic spectral analysis, with the help of which it is possible to quantitatively determine the content of various elements in a sample of a substance decomposed into atoms or ions in a flame or in an electric arc. Even before the creation of a quantitative version of this method, it was successfully used for “elemental analysis” of celestial bodies. Spectral analysis already in the last century helped to study the composition of the Sun and other stars, as well as to discover some elements, in particular helium.

With the help of spectral analysis, it became possible to distinguish not only different chemical elements, but also isotopes of the same element, which usually give different spectra. The method is used to analyze the isotopic composition of substances and is based on different shifts in the energy levels of molecules with different isotopes.

X-rays, named after the German physicist W. Roentgen who discovered them in 1895, are one of the shortest wavelength parts of the full spectrum of electromagnetic waves, located in it between ultraviolet light and gamma radiation. When X-rays are absorbed by atoms, deep electrons located near the nucleus and bound to it especially tightly are excited. The emission of X-rays by atoms, on the contrary, is associated with transitions of deep electrons from excited energy levels to ordinary, stationary ones.

Both levels can have only strictly defined energies, depending on the charge of the atomic nucleus. This means that the difference between these energies, equal to the energy of the absorbed (or emitted) quantum, also depends on the charge of the nucleus, and the radiation of each chemical element in the X-ray region of the spectrum is a set of waves characteristic of this element with strictly defined vibration frequencies.

X-ray spectral analysis, a type of elemental analysis, is based on the use of this phenomenon. It is widely used for the analysis of ores, minerals, as well as complex inorganic and organoelement compounds.

There are other types of spectroscopy based not on radiation, but on the absorption of light waves by matter. So-called molecular spectra are observed, as a rule, when solutions of substances absorb visible, ultraviolet or infrared light; In this case, no decomposition of molecules occurs. If visible or ultraviolet light usually acts on electrons, causing them to rise to new, excited energy levels (see Atom), then infrared (thermal) rays, which carry less energy, excite only vibrations of interconnected atoms. Therefore, the information that these types of spectroscopy provide chemists is different. If from the infrared (vibrational) spectrum one learns about the presence of certain groups of atoms in a substance, then spectra in the ultraviolet (and for colored substances - in the visible) region carry information about the structure of the light-absorbing group as a whole.

Among organic compounds, the basis of such groups, as a rule, is a system of unsaturated bonds (see Unsaturated hydrocarbons). The more double or triple bonds in a molecule, alternating with simple ones (in other words, the longer the conjugation chain), the easier the electrons are excited.

Molecular spectroscopy methods are used not only to determine the structure of molecules, but also to accurately measure the amount of a known substance in a solution. Spectra in the ultraviolet or visible region are especially convenient for this. Absorption bands in this region are usually observed at a solute concentration of the order of hundredths and even thousandths of a percent. A special case of such an application of spectroscopy is the colorimetry method, which is widely used to measure the concentration of colored compounds.

Atoms of some substances are also capable of absorbing radio waves. This ability manifests itself when a substance is placed in the field of a powerful permanent magnet. Many atomic nuclei have their own magnetic moment - spin, and in a magnetic field nuclei with unequal spin orientation turn out to be energetically “unequal”. Those whose spin direction coincides with the direction of the applied magnetic field find themselves in a more favorable position, and other orientations begin to play the role of “excited states” in relation to them. This does not mean that a nucleus in a favorable spin state cannot go into an “excited” state; the difference in the energies of the spin states is very small, but still the percentage of nuclei in an unfavorable energy state is relatively small. And the more powerful the applied field, the smaller it is. The nuclei seem to oscillate between two energy states. And since the frequency of such oscillations corresponds to the frequency of radio waves, resonance is also possible - the absorption of energy from an alternating electromagnetic field with the corresponding frequency, leading to a sharp increase in the number of nuclei in an excited state.

This is the basis for the work of nuclear magnetic resonance (NMR) spectrometers, capable of detecting the presence in a substance of those atomic nuclei whose spin is equal to 1/2: hydrogen 1H, lithium 7Li, fluorine 19F, phosphorus 31P, as well as isotopes of carbon 13C, nitrogen 15N, oxygen 17O, etc.

The more powerful the permanent magnet, the higher the sensitivity of such devices. The resonant frequency needed to excite nuclei also increases in proportion to the magnetic field strength. It serves as a measure of the class of the device. Middle class spectrometers operate at a frequency of 60-90 MHz (when recording proton spectra); cooler ones - at a frequency of 180, 360 and even 600 MHz.

High-class spectrometers - very accurate and complex instruments - make it possible not only to detect and quantitatively measure the content of a particular element, but also to distinguish the signals of atoms occupying chemically “unequal” positions in the molecule. And by studying the so-called spin-spin interaction, which leads to the splitting of signals into groups of narrow lines under the influence of the magnetic field of neighboring nuclei, one can learn a lot of interesting things about the atoms surrounding the nucleus under study. NMR spectroscopy allows you to obtain from 70 to 100% of the information needed, for example, to establish the structure of a complex organic compound.

Another type of radio spectroscopy - electron paramagnetic resonance (EPR) - is based on the fact that not only nuclei, but also electrons have a spin of 1/2. EPR spectroscopy is the best way to study particles with unpaired electrons - free radicals. Like NMR spectra, EPR spectra make it possible to learn a lot not only about the “signaling” particle itself, but also about the nature of the atoms surrounding it. EPR spectroscopy instruments are very sensitive: to record the spectrum, a solution containing several hundred millionths of a mole of free radicals per liter is usually quite sufficient. And a device with record sensitivity, recently created by a group of Soviet scientists, is capable of detecting the presence of only 100 radicals in a sample, which corresponds to their concentration of approximately 10 -18 mol/l.