The set of monochromatic components in radiation is called spectrum.

Emission spectra

Spectral composition radiation of substances is very diverse. But despite this, all spectra, as experience shows, can be divided into three types.

Continuous spectra

Continuous spectrumIt is a continuous multi-colored stripe.

White light has continuous spectrum. The solar spectrum or arc light spectrum is continuous. This means that the spectrum contains waves of all wavelengths. There are no breaks in the spectrum, and a continuous multi-colored strip can be seen on the spectrograph screen.

Continuous (or continuous) spectra, as experience shows, are given by bodies in the solid or liquid state, as well as highly compressed gases. To obtain a continuous spectrum, you need to heat the body to high temperature. A continuous spectrum is also produced by high-temperature plasma. Electromagnetic waves emitted by plasma mainly when electrons collide with ions.

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 to a strong extent depend on the interaction of atoms with each other.

Radiation from sources in which light is emitted by atoms of matter has discrete spectrum . They are divided into:

1. ruled

2. striped

Line spectra

Line spectrum consists of individual colored lines of varying brightness, separated by wide dark stripes.

Let's add a piece of asbestos moistened with a solution of ordinary table salt into the pale flame of a gas burner. When observing a flame through a spectroscope, a bright yellow line will flash against the background of the barely visible continuous spectrum of the flame. This yellow line is produced by sodium vapor, which is formed when the molecules of table salt are broken down in a flame. The figure also shows the spectra of hydrogen and helium. Such spectra are called line spectra. The presence of a line spectrum means that a substance emits light only at certain wavelengths (more precisely, in certain very narrow spectral intervals).

Line spectra give all substances in the gaseous atomic (but not molecular) state. In this case, light is emitted by atoms that practically do not interact with each other. This is the most fundamental, basic type of spectra.

Isolated atoms emit strictly defined wavelengths.

Typically, to observe line spectra, the glow of vapor of a substance in a flame or the glow of a gas discharge in a tube filled with the gas under study is used.

As the density of the atomic gas increases, the individual spectral lines expand, and finally, with very high compression of the gas, when the interaction of atoms becomes significant, these lines overlap each other, forming a continuous spectrum.

Striped spectra

Band spectrum consists of separate stripes separated by dark spaces.

With the help of a very good spectral apparatus it can be discovered that each band represents a collection large number very closely spaced lines. Unlike line spectra striped spectra are created not atoms, but molecules that are unbound or weakly bound to each other.

To observe molecular spectra, as well as to observe line spectra, the glow of vapor in a flame or the glow of a gas discharge is usually used.

Absorption spectra

All substances whose atoms are in an excited state emit light waves, the energy of which in a certain way distributed over wavelengths. The absorption of light by a substance also depends on the wavelength. Thus, red glass transmits waves corresponding to red light and absorbs all others.

If you pass white light through a cold, non-emitting gas, dark lines appear against the background of the continuous spectrum of the source. This will be the absorption spectrum.

Absorption spectrumrepresents dark lines against the background of the continuous spectrum of the source.

Gas absorbs most intensely the light of precisely those wavelengths that it emits when highly heated. Dark lines against the background of a continuous spectrum are absorption lines that together form an absorption spectrum.

There are continuous, line and striped absorption spectra.

Various types of electromagnetic radiation, their properties and practical applications.

Electromagnetic wave scale. The boundaries between different ranges are arbitrary

Low frequency vibrations.

Direct current - frequency ν = 0 – 10 Hz.

Atmospheric interference and alternating current - frequency ν = 10 – 10 4 Hz

Radio waves.

Frequency ν =10 4 – 10 11 Hz

Wavelength λ = 10 -3 – 10 3 m

Obtained using oscillatory circuits.

Properties.

Radio waves of different frequencies and with different wavelengths are absorbed and reflected differently by media, and exhibit diffraction and interference properties.

Application.

Radio communications, television, radar.

Infrared radiation.

Frequency ν =3·10 11 – 4·10 14 Hz

Wavelength λ = 8·10 -7 – 2·10 -3 m

Emitted by atoms and molecules of matter.

Infrared radiation is emitted by all bodies at any temperature. A person emits electromagnetic waves λ ≈ 9·10 -6 m.

Properties.

• Passes through some opaque bodies, as well as through snow, rain, and haze.
• Produces a chemical effect on photographic plates.
• When absorbed by a substance, it heats it up.
• Causes an internal photoelectric effect in germanium.
• Invisible.
• Capable of interference and diffraction phenomena.
• Recorded by thermal, photoelectric and photographic methods.

Application.

Obtain images of objects in the dark, with night vision devices, and in fog. Used in forensics, physiotherapy. in industry for drying painted products, building walls, wood, fruit.

Visible radiation.

Part electromagnetic radiation, perceived by the eye (from red to violet).

Frequency ν =4·10 14 – 8·10 14 Hz

Wavelength λ = 8·10 -7 – 4·10 -7 m

Properties.

It is reflected, refracted, affects the eye, and is capable of the phenomena of dispersion, interference, and diffraction.

Ultraviolet radiation.

Frequency ν =8·10 14 – 3·10 15 Hz

Wavelength λ = 10 -8 – 4 10 -7 m(but less than violet light)

Sources: gas-discharge lamps with quartz tubes (quartz lamps).

Radiated by everyone solids, for which t > 1000°С, as well as luminous mercury vapor.

Properties.

• High chemical activity (decomposition of silver chloride, glow of zinc sulfide crystals).
• Invisible.
• Kills microorganisms.
• In small doses it has a beneficial effect on the human body (tanning), but in large doses it has a negative biological effect: changes in cell development and metabolism, effects on the eyes.

Application.

In medicine, in cosmetology (solarium, tanning), in industry.

X-rays.

Frequency ν =3·10 15 – 3·10 19 Hz

Wavelength λ = 10 -11 – 4 10 -8 m

They are emitted when electrons moving with high acceleration are suddenly slowed down.

Obtained using an X-ray tube: electrons in a vacuum tube are accelerated electric field at high voltage, reaching the anode, they are sharply braked upon impact. When braking, electrons move with acceleration and emit electromagnetic waves with a short length (from 100 to 0.01 nm).

Properties.

• Interference, diffraction of x-rays on a crystal lattice.
• Great penetrating power.
• Irradiation in large doses causes radiation sickness.

Application.

In medicine (diagnosis of diseases internal organs), in industry (control internal structure various products, welds).

Gamma radiation (γ – radiation).

Frequency ν =3·10 20 Hz and above

Wavelength λ =3.3·10 -11 m

Sources: atomic nucleus (nuclear reactions).

Properties.

• Has enormous penetrating power.
• Has a strong biological effect.

Application.

In medicine, in production (γ - flaw detection).

Continuous spectra

We know that with the help spectral device(prism or diffraction grating) it is possible to “force” rays of light corresponding different lengths waves, go By different directions . If all wavelengths are represented in light, then on the screen we get continuous spectrum, in which there are all colors from red to violet, which smoothly transform into one another (Fig. 24.1).

Rice. 24.1

Rice. 24.2

Light intensity distribution over frequencies in the continuous spectrum has the character shown in Fig. 24.2. As the temperature increases, the maximum radiation intensity shifts towards higher high frequencies, and when decreasing - towards lower ones.

Such spectra are given by all luminous bodies if they are in hard or liquid condition (for example, an incandescent lamp). Sunlight, as we know, also has a continuous spectrum. Continuous spectra are also produced by highly compressed gases.

We will get a completely different picture if we pass the light emanating from luminous objects through a spectral device. rarefied gases. For example, sodium vapor gives one bright yellow line (and that’s it!) (Fig. 24.3, 1). The spectrum of atomic hydrogen gives four clear lines (Fig. 24.3, 2), and the spectrum of helium gives seven lines (Fig. 24.3, 3). You can make a gas glow only by heating it to high temperatures or passing an electric discharge through it.

Spectra consisting of individual lines are called ruled. Experience shows that line spectra give rare gases that are in the atomic (but not molecular) state. The line spectrum of each chemical element is strictly individual and does not match the spectrum of any other element. In a sense, it resembles human fingerprints: just as a criminal can be found by fingerprints, so by the presence of certain lines in the spectrum one can learn about the presence of a certain element in the substance under study.

Based on this spectral analysis – a method for determining the chemical composition of a substance from its spectrum.

Currently, the spectra of all atoms are known, therefore, having obtained the spectrum of an unknown substance, it is possible to determine which elements are included in the composition of this substance. Note that some elements (helium, rubidium, cesium, thallium, indium, gallium) were discovered using spectral analysis. It was by the method of spectral analysis that scientists were able to establish chemical composition Sun and stars.

Reader: And what spectra do they give? molecules made up of several atoms?

The banded spectrum consists of individual bands separated by dark spaces. With the help of a very good spectral apparatus one can discover that each band is a collection of a large number of very closely spaced lines.

Absorption spectra

We have found out that the atoms of each substance in an excited (highly heated) state emit light waves of a strictly defined length. The question arises: how do these same atoms absorb light waves? That is, what will we see if we pass white light containing waves of any length through a cold non-emitting gas?

The experiment shows that gas absorbs most intensively precisely those light waves that it emits in a highly heated state. Dark lines against the background of a continuous spectrum are absorption lines, forming absorption spectrum(see Fig. 24.3, 4–6).

Question 5. Types of spectra. Spectral analysis.

Spectral composition of atomic radiation various substances very diverse. However, all spectra can be divided into three very different types.

Continuous (solid) spectra. The continuous radiation spectrum (Fig. 19.12.1) contains waves of all lengths. There are no breaks in the spectrum, and on the spectrograph screen you can see a continuous multi-colored strip with a smooth transition from one color to another.

Continuous (or solid) spectra are given by bodies in the solid or liquid state, as well as highly compressed gases. To obtain a continuous spectrum, the body must be heated to a high temperature. 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 to a strong extent depend on the interaction of atoms with each other. A continuous spectrum is also produced by high-temperature plasma. Electromagnetic waves are emitted by plasma mainly when electrons collide with ions.

Line spectra. Line emission spectra (Fig. 19.13.2,3,4) are a set of colored lines of varying brightness, separated by wide dark stripes. The presence of a line spectrum means that a substance emits light only at certain wavelengths (more precisely, in certain very narrow spectral intervals). Each line has a finite width. Line spectra give all substances in the gaseous atomic (but not molecular) state. Isolated atoms of a chemical element emit strictly defined wavelengths characteristic of this chemical element. The nature of line spectra is explained by the fact that the atoms of a particular substance have only stationary states characteristic of it with their own set of energy levels.

Typically, to observe line spectra, the glow of vapor of a substance in a flame or the glow of a gas discharge in a tube filled with the gas under study is used. As the density of the atomic gas increases, the individual spectral lines expand and, at very high gas densities, when the interaction of atoms becomes significant, these lines overlap each other, forming a continuous spectrum.

Striped spectra. Banded emission spectra consist of individual bands separated by dark spaces (Fig. 19.14 : a, b).

With the help of a very good spectral instrument it can be discovered that each band is a collection of a large number of very closely spaced lines. Unlike line spectra, striped spectra are created not by atoms, but by molecules that are not bound or weakly bound to each other.

Absorption spectra. If white light is passed through a cold, non-emitting gas, dark absorption lines appear against the background of the continuous spectrum of the source (Fig. 19.15). Gas absorbs most intensely the light of precisely those wavelengths that it emits when highly heated. Dark lines against the background of a continuous spectrum are absorption lines that together form an absorption spectrum. Absorption spectra can be continuous, line or striped.

An atom, absorbing light, passes from the ground state to an excited one, and strictly defined energy quanta corresponding to a given gas are suitable for excitation of atoms. Therefore, the gas absorbs from the continuous spectrum the very quanta of light that it can emit itself.

Optical spectra

Emission spectra

400 450 500 550 600 700 (nm)

(1−solid; lined: 2−sodium; 3−hydrogen; 4−helium)

Striped spectra

Vapor emission spectrum of iodine molecules

Carbon arc emission spectrum (molecular bands CN And WITH 2)

Absorption spectra

400 450 500 550 600 700 (nm)

(5−solar; lined: 6−sodium; 7−hydrogen; 8−helium)

Figures 19.13 and 19.15 compare the emission and absorption spectra of rarefied vapors of sodium, hydrogen and helium.

By studying the emission and absorption spectra of atoms, back in the 19th century, physicists came to the conclusion that the atom is not an indivisible particle, but has some internal complex structure.

The use of line spectra is the basis spectral analysis – a method for studying the chemical composition of substances using their spectra. Individual lines in spectra various elements may coincide, but in general the spectrum of each element is its individual characteristic. Spectral analysis has played a major role in science. For example, in the spectrum of the Sun (1814), Fraunhofer dark lines were discovered, the origin of which is explained as follows. The Sun, being a hot ball of gas (T ~ 6000 °C), emits a continuous spectrum. sun rays pass through the atmosphere of the Sun (solar corona, the temperature of which is ~(2000–3000) °C. The corona absorbs radiation of a certain frequency from the continuous spectrum, and the solar absorption spectrum is recorded on Earth (Fig. 19.15.5), from which it is possible to determine which chemical elements are present in the corona of the Sun. Based on absorption spectra, all terrestrial elements were discovered on the Sun, as well as a previously unknown element, which was called helium. After 26 years (1894), helium was discovered on Earth. Thanks to spectral analysis, another 25 were discovered on Earth. chemical elements.

Moreover, spectral analysis of the Sun and stars showed that the chemical elements included in their composition are also present on Earth, i.e. The matter of the Universe consists of the same set of elements.

Due to its comparative simplicity and versatility, spectral analysis is the main method for monitoring the composition of a substance in metallurgy and mechanical engineering. Using spectral analysis, the chemical composition of ores and minerals is determined from both emission and absorption spectra. The composition of complex mixtures is analyzed using molecular spectra.

Under certain conditions, spectral analysis methods can not only determine the chemical composition of the components, but also their quantitative content.

Security questions:

1. Give Balmer’s formula and explain its physical meaning.

2. Why, of the various series of spectral lines of the hydrogen atom, was the Balmer series studied first?

3. What series of spectral lines do you know?

4. What is the emission frequency of the hydrogen atom corresponding to the short-wave boundary of the Bracket series?

5. Draw and explain a diagram of the energy levels of the hydrogen atom.

6. Give a diagram of Rutherford’s experiment and explain it.

7. What are Bohr's postulates? What is their physical meaning? How do they explain the line spectrum of an atom?

8. What are stationary orbits? How are their radii calculated?

9. Why did Rutherford’s nuclear model of the atom fail?

10. Give a diagram of the Frank and Hertz experiment and a current-voltage characteristic that describes the result of this experiment.

11. Which postulates of Bohr were confirmed by the experiments of Frank and Hertz?

12. What main conclusions can be drawn based on the experiments of Frank and Hertz?

13. Using the Bohr model, indicate the spectral lines that can arise during the transition of a hydrogen atom from states with n=3 and s n= 4.

14. Name the types of emission spectra. Describe the conditions for obtaining each type of spectra.

15. What is the absorption spectrum? Conditions for obtaining absorption spectra.

16. What is the basis of spectral analysis?

Thin Lens Formula

The thin lens formula relates d (the distance from the object to the optical center of the lens), f (the distance from the optical center to the image) with focal length F (Fig. 101).

Triangle ABO is similar to triangle OB 1 A 1. From the similarity it follows that

Triangle OCF is similar to triangle FB 1 A 1 . From the similarity it follows that

This is the thin lens formula.

Distances F, d and f from the lens to real points are taken with a plus sign, distances from the lens to imaginary points - with a minus sign.

The ratio of the image size H to the linear size of the object h is called the linear magnification of the lens G.

The spectral composition of radiation from substances is very diverse. But despite this, all spectra, as experience shows, can be divided into three types.

Continuous spectra. The solar spectrum or arc light spectrum is continuous. This means that the spectrum contains waves of all wavelengths. There are no breaks in the spectrum, and a continuous multi-colored strip can be seen on the spectrograph screen (see Fig. V, 1 on the color insert).

The distribution of energy over frequencies, i.e., the spectral density of radiation intensity, is different for different bodies. For example, a body with a very black surface emits electromagnetic waves of all frequencies, but the curve of the dependence of the spectral density of radiation intensity on frequency has a maximum at a certain frequency Vmax (Fig. 10.3). The radiation energy at very low (V -> 0) and very high (v -> v) frequencies is negligible. As body temperature increases, the maximum spectral radiation density shifts toward shorter waves.

Continuous (or continuous) spectra, as experience shows, give bodies that are in a solid or liquid state, as well as highly compressed gases. To obtain a continuous spectrum, the body must be heated to a high temperature.

The nature of the continuous spectrum and the very fact of its existence are not only determined by the properties of individual emitting atoms, but also strongly depend on the interaction of atoms with each other.

A continuous spectrum is also produced by high-temperature plasma. Electromagnetic waves are emitted by plasma mainly when electrons collide with ions.

Line spectra. Let's add a piece of asbestos moistened with a solution of ordinary table salt into the pale flame of a gas burner. When observing the flame through a spectroscope, we will see how a bright yellow line flashes against the background of the barely visible continuous spectrum of the flame (see Fig. V, 2 on the color insert).

This yellow line is produced by sodium vapor, which is formed when the molecules of table salt are broken down in a flame. The color insert also shows the spectra of hydrogen and helium. Each of the spectra is a palisade of colored lines of varying brightness, separated by wide dark stripes. Such spectra are called line spectra. The presence of a line spectrum means that a substance emits light only at certain wavelengths (more precisely, in certain very narrow spectral intervals). Figure 10.4 shows the approximate distribution of the spectral density of radiation intensity in a line spectrum. Each line has a finite width.

Line spectra give all substances in the gaseous atomic (but not molecular) state. In this case, light is emitted by atoms that practically do not interact with each other. This is the most fundamental, basic type of spectra.

Isolated atoms emit light at strictly defined wavelengths.

Typically, to observe line spectra, the glow of vapor of a substance in a flame or the glow of a gas discharge in a tube filled with the gas under study is used.

As the density of the atomic gas increases, the individual spectral lines expand, and finally, with very high compression of the gas, when the interaction of atoms becomes significant, these lines overlap each other, forming a continuous spectrum.

Striped spectra. The banded spectrum consists of individual bands separated by dark spaces. With the help of a very good spectral apparatus one can discover that each band is a collection of a large number of very closely spaced lines. Unlike line spectra, striped spectra are formed not by atoms, but by molecules that are not bound or weakly bound to each other.

To observe molecular spectra, as well as to observe line spectra, use the glow of vapor of a substance in a flame or the glow of a gas discharge.

Absorption spectra. All substances whose atoms are in an excited state emit light waves. The energy of these waves is distributed in a certain way across wavelengths. The absorption of light by a substance also depends on the wavelength. Thus, red glass transmits waves corresponding to red light (8 10 -5 cm), and absorbs all others.

If you pass white light through a cold, non-emitting gas, then dark lines appear against the background of the continuous spectrum of the source (see Fig. V, 5-8 on the color insert). Gas absorbs most intensely the light of precisely those wavelengths that it itself emits in a highly heated state. Dark lines against the background of a continuous spectrum are absorption lines that together form an absorption spectrum.

There are continuous, line and striped emission spectra and the same number of types of absorption spectra.

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, mass and energy distributions 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.

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 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 red-hot 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 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 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 needed by atoms to emit light can also come from non-thermal sources. During a discharge in gases, the electric field imparts a large force to the electrons. kinetic energy. 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. 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 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 filter, this liquid begins to glow with green-yellow light, i.e. longer length waves than that of 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 (which has the shortest wavelength in the visible spectrum (φ = 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 judge from it the amount of energy absorbed per unit time.

An ordinary thermometer is too insensitive 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. By 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 Av intervals, 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 devices. For accurate study of spectra, such simple devices as a narrow slit limiting the light beam and a prism are no longer sufficient. Instruments are needed that provide a clear spectrum, i.e., instruments that well separate waves of different lengths and do not allow individual parts of the spectrum to overlap. Such devices are called spectral devices. Most often, the main part of the spectral apparatus is a prism or diffraction grating.

Let us consider the design diagram of a prism spectral apparatus. The radiation under study first enters a part of the device called a collimator. The collimator is a tube, at one end of which there is a screen with a narrow slit, and at the other - a collecting lens. The slit is at the focal length of the lens. Therefore, a diverging light beam incident on the lens from the slit emerges from it as a parallel beam and falls on the prism.

Since different frequencies correspond to different refractive indices, parallel beams that do not coincide in direction emerge from the prism. They fall on the lens. At the focal length of this lens there is a screen - frosted glass or

photographic plate. The lens focuses parallel beams of rays on the screen, and instead of one image of the slit, a whole series of images is obtained. Each frequency (narrow spectral interval) has its own image. All these images together form a spectrum.

The described device is called a spectrograph. If, instead of a second lens and screen, a telescope is used to visually observe spectra, then the device is called a spectroscope, described above. Prisms and other parts of spectral devices are not necessarily made of glass. Instead of glass, transparent materials such as quartz, rock salt, etc. are also used.

Types of spectra

The spectral composition of radiation from substances is very diverse. But, despite this, all spectra, as experience shows, can be divided into several types:

Continuous spectra. The solar spectrum or arc light spectrum is continuous. This means that the spectrum contains waves of all wavelengths. There are no breaks in the spectrum, and a continuous multi-colored strip can be seen on the spectrograph screen.

The distribution of energy over frequencies, i.e., the spectral density of radiation intensity, is different for different bodies. For example, a body with a very black surface emits electromagnetic waves of all frequencies, but the curve of the dependence of the spectral density of radiation intensity on frequency has a maximum at a certain frequency. The radiation energy at very low and very high frequencies is negligible. With increasing temperature, the maximum spectral density of radiation shifts towards shorter waves.

Continuous (or continuous) spectra, as experience shows, are given by bodies in the solid or liquid state, as well as highly compressed gases. To obtain a continuous spectrum, the body must be heated to a high temperature.

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 to a strong extent depend on the interaction of atoms with each other.

A continuous spectrum is also produced by high-temperature plasma. Electromagnetic waves are emitted by plasma mainly when electrons collide with ions.

Line spectra. Let's add a piece of asbestos moistened with a solution of ordinary table salt into the pale flame of a gas burner.

When observing a flame through a spectroscope, a bright yellow line will flash against the background of the barely visible continuous spectrum of the flame. This yellow line is produced by sodium vapor, which is formed when the molecules of table salt are broken down in a flame. Each of them is a palisade of colored lines of varying brightness, separated by wide dark

stripes. Such spectra are called line spectra. The presence of a line spectrum means that a substance emits light only at certain wavelengths (more precisely, in certain very narrow spectral intervals). Each line has a finite width.

Line spectra give all substances in the gaseous atomic (but not molecular) state. In this case, light is emitted by atoms that practically do not interact with each other. This is the most fundamental, basic type of spectra.

Isolated atoms emit strictly defined wavelengths. Typically, to observe line spectra, the glow of vapor of a substance in a flame or the glow of a gas discharge in a tube filled with the gas under study is used.

As the density of the atomic gas increases, the individual spectral lines expand, and finally, with very high compression of the gas, when the interaction of atoms becomes significant, these lines overlap each other, forming a continuous spectrum.

Striped spectra. The banded spectrum consists of individual bands separated by dark spaces. With the help of a very good spectral apparatus it is possible

discover that each stripe is a collection of a large number of very closely spaced lines. Unlike line spectra, striped spectra are created not by atoms, but by molecules that are not bound or weakly bound to each other.

To observe molecular spectra, as well as to observe line spectra, the glow of vapor in a flame or the glow of a gas discharge is usually used.

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. Thus, red glass transmits waves corresponding to red light and absorbs all others.

If you pass white light through a cold, non-emitting gas, dark lines appear against the background of the continuous spectrum of the source. Gas absorbs most intensely the light of precisely those wavelengths that it emits when highly heated. Dark lines against the background of a continuous spectrum are absorption lines that together form an absorption spectrum.

There are continuous, line and striped emission spectra and the same number of types of absorption spectra.

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. Therefore, by becoming familiar with line spectra, we thereby take the first step towards studying the structure of atoms. By observing these spectra, scientists obtained

the opportunity to “look” inside the atom. Here optics comes into close contact with atomic physics.

Types of spectral analyzes

The main property of line spectra is that the wavelengths (or frequencies) of the line spectrum of any substance depend only on the properties of the atoms of this substance, but are completely independent of the method of excitation of the luminescence of the atoms. Atoms

any chemical element gives a spectrum that is not similar to the spectra of all other elements: they are capable of emitting a strictly defined set of wavelengths.

This is the basis of spectral analysis - a method of determining the chemical composition of a substance from its spectrum. Like human fingerprints, line spectra have a unique personality. The uniqueness of the patterns on the skin of the finger often helps to find the criminal. In the same way, due to the individuality of the spectra, there is

the ability to determine the chemical composition of the body. Using spectral analysis, you can detect this element as part of a complex substance. This is a very sensitive method.

Currently known the following types spectral analyzes - atomic spectral analysis (ASA)(determines the elemental composition of a sample from atomic (ion) emission and absorption spectra), emission ASA(based on the emission spectra of atoms, ions and molecules excited by various sources of electromagnetic radiation in the range from g-radiation to microwave), atomic absorption SA(carried out using the absorption spectra of electromagnetic radiation by the analyzed objects (atoms, molecules, ions of matter in various states of aggregation)), atomic fluorescence SA, molecular spectral analysis (MSA) (molecular composition of substances according to molecular spectra of absorption, luminescence and Raman scattering of light.), quality ISA(it is enough to establish the presence or absence of analytical lines of the elements being determined. Based on the brightness of the lines during visual inspection, one can give a rough estimate of the content of certain elements in the sample), quantitative ISA(carried out by comparing the intensities of two spectral lines in the spectrum of the sample, one of which belongs to the element being determined, and the other (comparison line) to the main element of the sample, the concentration of which is known, or an element specially introduced at a known concentration).

MSA is based on a qualitative and quantitative comparison of the measured spectrum of the sample under study with the spectra of individual substances. Accordingly, a distinction is made between qualitative and quantitative ISA. MSA uses various types of molecular spectra, rotational [spectra in the microwave and long-wave infrared (IR) regions], vibrational and vibrational-rotational [absorption and emission spectra in the mid-IR region, Raman spectra, IR fluorescence spectra ], electronic, electronic-vibrational and electronic-vibrational-rotational [absorption and transmission spectra in the visible and ultraviolet (UV) regions, fluorescence spectra]. MSA allows analysis of small quantities (in some cases a fraction mcg and less) substances in different states of aggregation.

Quantitative analysis of the composition of a substance based on its spectrum is difficult, since the brightness of the spectral lines depends not only on the mass of the substance, but also on the method of excitation of the glow. Thus, at low temperatures, many spectral lines do not appear at all. However, subject to standard conditions for excitation of the glow, quantitative spectral analysis can also be carried out.

The most accurate of these tests is atomic absorption SA. The AAA technique is much simpler compared to other methods; it is characterized by high accuracy in determining not only small, but also large concentrations of elements in samples. AAA successfully replaces labor-intensive and time-consuming chemical analysis methods without being inferior to them in accuracy.

Conclusion

Currently, the spectra of all atoms have been determined and tables of the spectra have been compiled. With the help of spectral analysis, many new elements were discovered: rubidium, cesium, etc. Elements were often given names in accordance with the color of the most intense lines in the spectrum. Rubidium produces dark red, ruby ​​lines. The word cesium means "sky blue". This is the color of the main lines of the spectrum of cesium.

It was with the help of spectral analysis that the chemical composition of the Sun and stars was learned. Other methods of analysis are generally impossible here. It turned out that stars consist of the same chemical elements that are found on Earth. It is curious that helium was originally discovered in the Sun, and only then found in the Earth's atmosphere. The name of this

element recalls the history of its discovery: the word helium means “solar” in translation.

Due to its comparative simplicity and versatility, spectral analysis is the main method for monitoring the composition of a substance in metallurgy, mechanical engineering, and the nuclear industry. Using spectral analysis, the chemical composition of ores and minerals is determined.

The composition of complex, mainly organic, mixtures is analyzed by their molecular spectra.

Spectral analysis can be performed not only from emission spectra, but also from absorption spectra. It is the absorption lines in the spectrum of the Sun and stars that make it possible to study the chemical composition of these celestial bodies. The brightly luminous surface of the Sun - the photosphere - produces a continuous spectrum. The solar atmosphere selectively absorbs light from the photosphere, which leads to the appearance of absorption lines against the background of the continuous spectrum of the photosphere.

But the atmosphere of the Sun itself emits light. During solar eclipses, when the solar disk is covered by the Moon, the lines of the spectrum are reversed. In place of absorption lines in the solar spectrum, emission lines flash.

In astrophysics, spectral analysis means not only the determination of the chemical composition of stars, gas clouds, etc., but also the determination of many

other physical characteristics of these objects: temperature, pressure, speed of movement, magnetic induction.

It is important to know what the bodies around us are made of. Many methods have been invented to determine their composition. But the composition of stars and galaxies can only be determined using spectral analysis.

Express ASA methods are widely used in industry, agriculture, geology and many other areas of the national economy and science. ASA plays a significant role in nuclear technology, the production of pure semiconductor materials, superconductors, etc. More than 3/4 of all analyzes in metallurgy are performed using ASA methods. Using quantum meters, an operational procedure is carried out (within 2-3 min) control during melting in open-hearth and converter production. In geology and geological exploration, about 8 million analyzes are performed per year to evaluate deposits. ASA is used for environmental protection and soil analysis, in forensics and medicine, seabed geology and the study of the composition of the upper atmosphere, with

separation of isotopes and determination of the age and composition of geological and archaeological objects, etc.

So, spectral analysis is used in almost all the most important areas of human activity. Thus, spectral analysis is one of the most important aspects of the development of not only scientific progress, but also the very standard of human life.

Literature

Zaidel A.N., Fundamentals of spectral analysis, M., 1965,

Methods of spectral analysis, M, 1962;

Chulanovsky V.M., Introduction to molecular spectral analysis, M. - L., 1951;

Rusanov A.K., Fundamentals of quantitative spectral analysis of ores and minerals. M., 1971