How is spectral analysis performed? School encyclopedia

Ministry of Education and Science
Republic of Kazakhstan

Karaganda State University
named after E.A. Buketova

Faculty of Physics

Department of Optics and Spectroscopy

Course work

on the topic of:

Spectra. WITH spectral analysis and its application.

Prepared by:

student of the FTRF-22 group

Akhtariev Dmitry.

Checked:

teacher

Kusenova Asiya Sabirgalievna

Karaganda - 2003 Plan

Introduction

1. Energy in the spectrum

2. Types of spectra

3. Spectral analysis and its application

4. Spectral devices

5. Spectrum of electromagnetic radiation

Conclusion

List of used literature

Introduction

Studying the line spectrum of a substance allows us to determine what chemical elements it consists of and in what quantity each element is contained in a given substance.

The quantitative content of an element in the sample under study is determined by comparing the intensity of individual lines in the spectrum of this element with the intensity of the lines of another chemical element, the quantitative content of which in the sample is known.

Method for determining quality and quantitative composition The analysis of a substance by its spectrum is called spectral analysis. Spectral analysis is widely used in mineral exploration to determine chemical composition ore samples. In industry, spectral analysis makes it possible to control the composition of alloys and impurities introduced into metals to obtain materials with specified properties.

Advantages spectral analysis are high sensitivity and speed of obtaining results. Using spectral analysis, it is possible to detect the presence of gold in a sample weighing 6 * 10 -7 g with its mass of only 10 -8 g. Determination of the steel grade by the method of spectral analysis can be performed in a few tens of seconds.

Spectral analysis allows you to determine the chemical composition celestial bodies, distant from Earth at distances of billions of light years. The chemical composition of the atmospheres of planets and stars, cold gas in interstellar space is determined from absorption spectra.

By studying the spectra, scientists were able to determine not only the chemical composition of celestial bodies, but also their temperature. By offset spectral lines you can determine the speed of movement of a celestial body.

Energy in the spectrum.

The light source must consume energy. Light is electromagnetic waves with a wavelength of 4*10 -7 - 8*10 -7 m. Electromagnetic waves 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) radiating body. The higher the body temperature, the faster the atoms move. When fast atoms (molecules) collide with each other, part of them kinetic energy converted into excitation energy of 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 in the lamp electric shock, 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 required for atoms to emit light can also be obtained 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. Glow solids, caused by bombardment by their electrons, is called cathodoluminescence. Thanks to cathodoluminescence, the screens of cathode ray tubes of televisions glow.

Chemiluminescence. For some chemical reactions, coming with the release of energy, part of this energy is directly spent on the emission of light. The light source remains cold (it has a temperature environment). 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 atoms of matter (increases their internal energy), after which they are highlighted 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 passed through a violet filter onto a vessel with fluoresceite (an organic dye), then 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 suggested covering inner surface discharge tube with substances capable of glowing brightly under the influence of short-wave radiation 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. None of the sources gives monochromatic light, i.e. light of a strictly defined wavelength. We are convinced of this by experiments on the 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 difference between wavelength and frequency. simple connection: ђv = c.

Flux density 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 emission spectrum, for example, 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 sensing element made in the form of a thin metal plate. This plate must be covered thin layer 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 find that most of energy falls on the red part of the spectrum, and not on 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.

Plotting along the abscissa axis the values of frequencies corresponding to the midpoints of the intervals Av, and along the ordinate axis spectral density radiation intensity, we get 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.

Spectral analysis is one of the most important physical methods substance research. 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 the incident incident on it. white light. In the second case, the color visible to the eye, turns out to correspond not to these absorbed waves, but to others - additional ones, giving white light when added to them.

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 which it is possible to quantitatively determine the content various elements in a sample of a substance decomposed into atoms or ions in a flame or 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 energy absorbed (or emitted) quantum also depends on the charge of the nucleus, and the emission of each chemical element in the X-ray region of the spectrum is characteristic of of this element a set of waves with strictly defined oscillation 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 elemental organic compounds.

There are other types of spectroscopy based not on radiation, but on the absorption of light waves by matter. The 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, carrying 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, than longer chain conjugation), 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 quantity known substance in 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 alternating energy 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 spectrometers. magnetic resonance(NMR), capable of detecting the presence of those substances atomic nuclei, the spin of which is 1/2: hydrogen 1H, lithium 7Li, fluorine 19F, phosphorus 31P, as well as isotopes of carbon 13C, nitrogen 15N, oxygen 17O, etc.

The sensitivity of such devices is higher, the more powerful they are. permanent magnet. 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 - The best way studies of 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: a solution containing a few hundred millionths of a mole is usually sufficient to record a spectrum. free radicals for 1 l. 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.

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 in studied objects the smallest quantities of the substance being determined (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 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 chemical content body by analyzing the chemical composition of the substance. Even if its mass of the element does not exceed 10 - 10 g, using spectral analysis it can be detected in the composition 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 analytical chemistry as a subject whose purpose 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 determining chemical substance, 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 deeper internal electronic layers lines appear x-ray radiation.

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 known distance d. This is the basis of the determination method. The substance being studied is bombarded with high-speed electrons. Place it, for example, on the anode of a collapsible x-ray tube, subsequently which it exudes characteristic X-rays that fall on the crystal 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 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 it physical properties, which depends on its content in the substance sample. 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, plotted in the coordinates: “saturation of a physical property - concentration of the component being installed.”

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. On chemical properties chemical compounds, based chemical interactions. 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 analysis physical and chemical composition substances 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.

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.

Method for studying chemical composition various substances according to their line emission or absorption spectra are 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 characteristic only for it line spectrum emission and absorption, this makes it possible to study the chemical composition of a 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 this, 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 color could mask the other. This allowed us to conclude that a radical new way chemical analysis - according to the spectrum of the 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.

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.

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.

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 refracting prism, monochromatic colors in the spectrum are arranged in the following order: red (which has the largest wavelength visible light wavelength (k=7.6(10-7 m and lowest rate refraction), orange, yellow, green, cyan, indigo and violet (having the shortest wavelength in the visible spectrum (f = 4 (10-7 m and highest rate refraction). None of the sources produces monochromatic light, that is, light of a strictly defined wavelength. We are convinced of this by experiments on the 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.

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.

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.

Spectral analysis is a method for studying the chemical composition of various substances using their spectra.

Analysis carried out using emission spectra is called emission spectral analysis, and analysis carried out using absorption spectra is called absorption spectral analysis.

Emission spectral analysis is based on the following facts:

1. Each element has its own spectrum (differing in the number of lines, their location and wavelengths), which does not depend on the methods of excitation.

2. The intensity of spectral lines depends on the concentration of the element in a given substance.

To perform a spectral analysis of a substance with an unknown chemical composition, it is necessary to carry out two operations: somehow force the atoms of this substance to emit light with a line spectrum, then decompose this light into a spectrum and determine the wavelengths of the lines observed in it. By comparing the resulting line spectrum with the known spectra of chemical elements of the periodic table, it is possible to determine which chemical elements are present in the composition of the substance under study. By comparing the intensities of different lines in the spectrum, the relative content of various elements in this substance can be determined.

Spectral analysis can be qualitative and quantitative.

If the substance under study is in a gaseous state, then to excite the atoms of the substance it is usually used spark discharge. A tube with two electrodes at the ends is filled with the gas under study. These electrodes are supplied high voltage and an electrical discharge occurs in the tube. Impacts of electrons accelerated electric field, lead to ionization and excitation of atoms of the gas under study. During transitions of excited atoms into normal condition quanta of light characteristic of a given element are emitted.

To determine the chemical composition of a substance located in a solid or liquid state, according to its emission spectrum, it is necessary to first convert the substance under study into gaseous state and somehow make this gas emit light. Typically, an arc discharge is used to carry out spectral analysis of samples of a substance in the solid state. In the arc plasma, the substance is converted into vapor, and atoms are excited and ionized. The electrodes between which the arc discharge is ignited are usually made of the substance under study (if it is metal) or of graphite or copper. Carbon and copper are chosen because the emission spectra of their atoms in the visible region have a small number of lines and, therefore, do not create serious interference in observing the spectrum of the substance under study. The powder of the test substance is placed in the recess of the lower electrode.

Literature

Aksenovich L. A. Physics in high school: Theory. Tasks. Tests: Textbook. allowance for institutions providing general education. environment, education / L. A. Aksenovich, N. N. Rakina, K. S. Farino; Ed. K. S. Farino. - Mn.: Adukatsiya i vyakhavanne, 2004. - P. 531-532.